10-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

(Mark One)

☑	ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
	For the fiscal year ended December 31, 2023
	OR
☐	TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
	For the transition period from _____________ to _____________

Commission file number 1-7414

Northwest Pipeline LLC

(Exact name of registrant as specified in its charter)

Delaware	26-1157701
(State or other jurisdiction of incorporation or organization)	(I.R.S. Employer Identification No.)
One Williams Center
Tulsa, Oklahoma	74172-0172
(Address of Principal Executive Offices)	(Zip Code)

Registrant’s telephone number, including area code: (800) 945-5426

Securities registered pursuant to Section 12(b) of the Act: None

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.  Yes  ¨    No  þ

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.  Yes  ¨    No  þ

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.  Yes  þ    No  ¨

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files).  Yes  þ    No  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer ☐ Accelerated filer ☐ Non-accelerated filer þ Smaller reporting company ☐ Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ¨

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. ¨

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements. ¨

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to §240.10D-1(b). ¨

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).  Yes  ☐     No  þ

DOCUMENTS INCORPORATED BY REFERENCE: None

THE REGISTRANT MEETS THE CONDITIONS SET FORTH IN GENERAL INSTRUCTIONS (I)(1)(a) AND (b) OF FORM 10-K AND IS THEREFORE FILING THIS FORM 10-K WITH THE REDUCED DISCLOSURE FORMAT.

NORTHWEST PIPELINE LLC

FORM 10-K

TABLE OF CONTENTS

		Page
	PART I
Item 1.	Business	3
	General	3
	Rate Matters	4
	Regulation	4
	Employees	6
	Transactions with Affiliates	6
Item 1A.	Risk Factors	6
Item 1B.	Unresolved Staff Comments	18
Item 1C.	Cybersecurity	18
Item 2.	Properties	20
Item 3.	Legal Proceedings	20
Item 4.	Mine Safety Disclosures	20
	PART II
Item 5.	Market For Registrant's Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities	21
Item 7.	Management's Discussion and Analysis of Financial Condition and Results of Operations	21
Item 7A.	Quantitative and Qualitative Disclosures About Market Risk	23
Item 8.	Financial Statements and Supplementary Data	24
Item 9.	Changes in and Disagreements With Accountants on Accounting and Financial Disclosure	47
Item 9A.	Controls and Procedures	47
Item 9B.	Other Information	48
Item 9C.	Disclosure Regarding Foreign Jurisdictions that Prevent Inspections	48
	PART III
Item 10.	Directors, Executive Officers and Corporate Governance (Omitted)	48
Item 11.	Executive Compensation (Omitted)	48
Item 12.	Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters (Omitted)	48
Item 13.	Certain Relationships and Related Transactions, and Director Independence (Omitted)	48
Item 14.	Principal Accountant Fees and Services	48
	PART IV
Item 15.	Exhibits and Financial Statement Schedules	49
Item 16.	Form 10-K Summary	51

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DEFINITIONS

The following is a listing of certain abbreviations, acronyms, and other industry terminology that may be used throughout this Annual Report.

Measurements:

Bcf: One billion cubic feet of natural gas

Dekatherms (Dth): A unit of energy equal to one million British thermal units

MMdth: One million dekatherms or approximately one trillion British thermal units

MMdth/d: One million dekatherms per day

Government and Regulatory:

EPA: U.S. Environmental Protection Agency

Exchange Act: Securities and Exchange Act of 1934, as amended

FERC: Federal Energy Regulatory Commission

NGA: Natural Gas Act of 1938, as amended

SEC: Securities and Exchange Commission

Securities Act: Securities Act of 1933, as amended

Other:

LNG: Liquefied natural gas; natural gas which has been liquefied at cryogenic temperatures

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PART I

Item 1. Business

In this report, Northwest Pipeline LLC (Northwest) is at times referred to in the first person as “we,” “us,” or “our.”

Northwest is indirectly owned by The Williams Companies, Inc. (Williams), a publicly traded Delaware corporation.

GENERAL

We own and operate a natural gas pipeline system that extends from the San Juan Basin in northwestern New Mexico and southwestern Colorado through the states of Colorado, Utah, Wyoming, Idaho, Oregon and Washington to a point on the Canadian border near Sumas, Washington. We provide natural gas transportation services for markets in Washington, Oregon, Idaho, Wyoming, Nevada, Utah, Colorado, New Mexico, California and Arizona, either directly or indirectly through interconnections with other pipelines. Our principal business is the interstate transportation of natural gas, which is regulated by FERC.

Our system includes approximately 3,900 miles of mainline and lateral transmission pipeline and 42 transmission compressor stations. Our compression facilities have a combined sea level-rated capacity of approximately 476,000 horsepower. At December 31, 2023, our natural gas pipeline had a design capacity of approximately 3.8 MMdth/d.

We own a one-third undivided interest in the Jackson Prairie underground storage facility located near Chehalis, Washington. We have a contract for natural gas storage services in an underground storage reservoir in the Clay Basin Field located in Daggett County, Utah. The owner of this storage field was acquired by Williams in February 2023. We also own and operate a LNG storage facility near Plymouth, Washington. We have approximately 13.5 Bcf of working natural gas storage capacity through these three storage facilities, which is substantially utilized for third-party natural gas. These natural gas storage facilities enable us to balance daily receipts and deliveries and provide storage services to our customers.

We transport and store natural gas for a broad mix of customers, including public utilities, municipalities, direct industrial users, electric power generators, and natural gas marketers and producers. We offer firm and interruptible transportation and storage service. Our firm transportation and storage contracts are generally long-term contracts with various expiration dates and account for the major portion of our business. During 2023, our three largest customers were Puget Sound Energy, Inc., Cascade Natural Gas Corporation, and Northwest Natural Gas Company, which accounted for approximately 29 percent, 11 percent, and 11 percent, respectively, of our total operating revenues for the year ended December 31, 2023. No other customer accounted for more than 10 percent of our total operating revenues during that period.

Our rates are subject to the rate-making policies of the FERC. We provide a significant portion of our transportation and storage services pursuant to long-term firm contracts that obligate our customers to pay us monthly capacity reservation fees, which are fees that are owed for reserving an agreed upon amount of pipeline or storage capacity regardless of the amount of pipeline or storage capacity actually utilized by a customer. When a customer utilizes the capacity it has reserved under a firm transportation contract, we also collect a volumetric fee based on the quantity of natural gas transported. These volumetric fees are typically a small percentage of the total fees received under a firm contract. We also derive a small portion of our revenues from short-term firm and interruptible contracts under which customers pay fees for transportation, storage and other related services. The high percentage of our revenue derived from capacity reservation fees helps mitigate the risk of revenue fluctuations caused by changing supply and demand conditions.

PIPELINE PROJECTS

The pipeline project listed below is a significant future pipeline project for which we have customer commitments. In 2024, we expect to invest capital of approximately $7 million in pipeline projects.

Ryckman Creek Loop

The Ryckman Creek Loop expansion involves an expansion of our existing natural gas transmission system to provide incremental firm transportation capacity from a receipt point in Northeast Oregon (Stanfield) to multiple delivery points in Southwest Wyoming. We plan to place the project in service as early as the fourth quarter of 2025 assuming timely receipt of all necessary regulatory approvals. The project is expected to increase capacity by 50.5 MDth/d.

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RATE MATTERS

FERC regulation requires all terms and conditions of service, including the rates charged, to be filed with and accepted by the FERC before any changes can go into effect. We establish our rates primarily through the FERC’s ratemaking process, but we also may negotiate rates with our customers pursuant to the terms of our tariff and FERC policy. Key determinants in the ratemaking process are (1) costs of providing service, including depreciation expense, (2) allowed rate of return, including the equity component of the capital structure and related income taxes, and (3) contract and volume throughput assumptions. The allowed rate of return is determined in each rate case. Rate design and the allocation of costs between the reservation and commodity rates also impact profitability. As a result of rate case proceedings, certain revenues may be collected subject to refund. We record estimates of rate refund liabilities considering our and third-party regulatory proceedings, advice of counsel, and other risks.

Rate Case Settlement

On November 15, 2022, the FERC approved our Petition for Approval of Pre-Filing Stipulation and Settlement Agreement (Settlement) in Docket No. RP22-1155. The Settlement established a new general system firm Rate Schedule TF-1 (Large Customer) daily reservation rate of $0.37250/Dth with a $0.00935/Dth commodity rate (which were made effective January 1, 2023), resolved other rate issues, established a Modernization and Emission Reduction Program and satisfied our rate case filing obligation under our settlement in Docket No. RP17-346. Provisions were included in the Settlement that establish a moratorium on any Natural Gas Act of 1938, as amended (NGA) Section 4 or 5 proceedings that would seek to place new rates in effect any earlier than January 1, 2026. The Settlement also provides that we file an NGA Section 4 general rate case with rates to be effective not later than April 1, 2028, unless (a) we have entered into a pre-filing settlement or (b) a Section 5 general rate case has been filed on or before April 1, 2028.

As a result of the Settlement, in January 2023, we refunded approximately $126 million, including interest, associated with the decrease in federal tax rates due to the Tax Cuts and Jobs Act of 2017 (Tax Reform), which reduced Accrued liabilities - Regulatory liabilities on our Balance Sheet.

                        REGULATION

FERC Regulation

Our interstate transmission and storage activities are subject to regulation by the FERC under the NGA, and under the Natural Gas Policy Act of 1978, as amended, and, as such, our rates and charges for the transportation of natural gas in interstate commerce, the extension, enlargement, or abandonment of jurisdictional facilities, and accounting, among other things, are subject to regulation. We hold certificates of public convenience and necessity issued by the FERC authorizing ownership and operation of pipelines, facilities, and properties for which certificates are required under the NGA. FERC Standards of Conduct govern the relationship between natural gas transmission providers and marketing function employees as defined by the rule. The Standards of Conduct are intended to prevent natural gas transmission providers from preferentially benefiting gas marketing functions by requiring the employees of a transmission provider that perform transmission functions to function independently from marketing function employees and by restricting the information that transmission providers may provide to marketing function employees. Under the Energy Policy Act of 2005, the FERC is authorized to impose civil penalties of up to approximately $1.5 million per day for each violation of its rules.

Updated Certificate Policy Statement and Interim Greenhouse Gas (GHG) Policy Statement On February 18, 2022, the FERC issued two policy statements providing guidance for its pending and future consideration of interstate natural gas pipeline projects. The first policy statement is an Updated Certificate Policy Statement, which provides an analytical framework for how the FERC will consider whether a project is in the public convenience and necessity and explains that the FERC will consider all impacts of a proposed project, including economic and environmental impacts, together. The second policy statement is an Interim GHG Policy Statement, which sets forth how the FERC will assess the impacts of natural gas infrastructure projects on climate change in its reviews under the National Environmental Policy Act and the NGA. The FERC sought comment on all aspects of the policy statements, including the approach to assessing the significance of the proposed project’s contribution to climate change. On March 24, 2022, the FERC issued an order converting the Updated Certificate Policy Statement and the Interim GHG Policy Statement into draft policy statements and announcing that it will not apply either policy statement to pending applications or applications filed before the FERC issues any final guidance on the policy statements. The FERC has not yet issued final guidance on the policy statements.

Environmental Matters

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Our operations are subject to federal environmental laws and regulations as well as the state and local laws and regulations adopted by the jurisdictions in which we operate. We could incur liability to governments or third parties for any unlawful discharge of pollutants into the air, soil, or water, as well as liability for cleanup costs. Materials could be released into the environment in several ways including, but not limited to:

•Leakage from underground gas storage caverns, pipelines, transportation facilities, and storage tanks;

•Damage to facilities resulting from accidents during normal operations;

•Damages to equipment and facilities resulting from storm events or natural disasters; and

•Blowouts, cratering, and explosions.

In addition, we may be liable for environmental damage caused by former owners or operators of our properties.

We believe compliance with current environmental laws and regulations will not have a material adverse effect on our capital expenditures, earnings, or current competitive position. However, environmental laws and regulations could affect our business in various ways from time to time, including incurring capital and maintenance expenditures, fines and penalties, and creating the need to seek relief from the FERC for rate increases to recover the costs of certain capital expenditures and operation and maintenance expenses.

Washington State Climate Commitment Act In 2021, the state of Washington passed its Climate Commitment Act establishing a market-based cap-and-invest program to reduce carbon emissions. This program took effect on January 1, 2023, and sets a limit, or cap, on overall carbon emissions in the state and requires businesses like ours to obtain allowances equal to their annual covered carbon emissions. The state’s cap will be reduced over time to meet the state’s carbon emissions reduction targets, which means fewer carbon emissions allowances will be available to purchase each year. These allowances can be purchased through quarterly auctions hosted by the state or bought and sold on a secondary market. In 2023, we began purchasing allowances for the carbon emissions from nine of our thirteen compressor stations within the state whose annual carbon emissions exceed 25,000 metric tons of carbon dioxide equivalent. We also began purchasing allowances for our delivery of natural gas to certain of our customers and certain of our facilities in the state whose annual carbon emissions are insufficient to require their direct participation in the program. Our Settlement allows us to recover the costs of purchasing allowances under the program in our next rate case.

For additional information regarding the potential impact of federal, state, or local regulatory measures on our business and specific environmental issues, please refer to “Risk Factors – Our operations are subject to environmental laws and regulations, including laws and regulations relating to climate change and greenhouse gas emissions, which may expose us to significant costs, liabilities, and expenditures that could exceed our expectations,” and “Environmental Matters” in Part II, Item 8. Financial Statements and Supplementary Data – Note 5 – Contingent Liabilities and Commitments of Notes to Financial Statements.

Safety and Maintenance

Our operations are subject to the Natural Gas Pipeline Safety Act of 1968, as amended, the Pipeline Safety Improvement Act of 2002, the Pipeline Safety, Regulatory Certainty, and Jobs Creation Act of 2011 (Pipeline Safety Act), and the Protecting Our Infrastructure of Pipelines and Enhancing Safety (PIPES Act) of 2016 and 2020, which regulate safety requirements in the design, construction, operation, and maintenance of interstate natural gas transmission facilities. The United States Department of Transportation Pipeline and Hazardous Materials Safety Administration (PHMSA) administers federal pipeline safety laws.

Federal pipeline safety laws authorize PHMSA to establish minimum safety standards for pipeline facilities and persons engaged in the transportation of gas or hazardous liquids by pipeline. These safety standards apply to the design, construction, testing, operation, and maintenance of gas and hazardous liquids pipeline facilities affecting interstate or foreign commerce. PHMSA has also established reporting requirements for operators of gas and hazardous liquid pipeline facilities, as well as provisions for establishing the qualification of pipeline personnel and requirements for managing the integrity of gas transmission and distribution lines and certain hazardous liquid pipelines. To ensure compliance with these provisions, PHMSA performs pipeline safety inspections and has the authority to initiate enforcement actions.

In August 2022, PHMSA published Rule 2, which is the last in the three part Mega Rule set of regulations. Rule 2 went into effect in May 2023 but a stay of enforcement until February 2024 limited the amount of the regulation that was implemented. Rule 2 contains new corrosion control requirements, new requirements for repair criteria outside of high consequence areas (HCAs), inspections to be performed after extreme weather events or natural disasters, management of change, and other integrity management related rule changes. Since the rule was published in 2022, we have worked to

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understand the regulatory changes and modify our procedures as needed. In total there have been more than 20 procedures and forms that have been modified to account for the Rule 2 changes. All procedures will be in effect when the February 2024 Stay of Enforcement expires.

In May 2023 PHMSA published the Gas Pipeline Leak Detection and Repair Notice of Proposed Rule Making (NPRM). While this regulation has not been published as final and is still subject to change, the rule could institute many new requirements including: increased survey and patrol frequencies, new timelines for repairing and mitigating leaks, strict performance standards for advanced leak detection programs, and other additional requirements focused on reducing methane emissions. We have been actively working to provide comments on the rule and are working to understand the overall impact if implemented as currently written.

Pipeline Integrity Regulations We have an enterprise-wide Gas Integrity Management Plan that meets the PHMSA final rule that was issued pursuant to the requirements of the Pipeline Safety Improvement Act of 2002. The rules require pipeline operators to develop an integrity management program for transmission pipelines that could affect HCAs in the event of pipeline failure. The integrity management program includes a baseline assessment plan along with periodic reassessments to be completed within required time frames. In meeting the integrity regulations, we have identified HCAs and developed baseline assessment plans. Ongoing periodic reassessments and initial assessments of any new HCAs have been completed. Also, in response to the portion of the Mega Rule implemented in 2021, we have identified Moderate Consequence Areas and Class 3 and 4 pipeline locations required by the rule and integrated those segments into our integrity program, and have begun scheduling required assessments and reassessments as needed to meet the regulatory timelines. We estimate that the cost to be incurred in 2024 associated with this program to be approximately $23 million. Management considers the costs associated with compliance with the rule to be prudent costs incurred in the ordinary course of business and, therefore, recoverable through our rates.

Cybersecurity Matters

The Transportation Security Administration (TSA) issued Security Directive Pipeline-2021-01C (Security Directive 1C) on May 29, 2023, which requires that owners/operators of critical pipelines (1) report cybersecurity incidents to the Cybersecurity and Infrastructure Agency (CISA) within 24 hours; (2) appoint a cybersecurity coordinator to coordinate with TSA and CISA; and (3) conduct a self-assessment of cybersecurity practices, identify any gaps, and develop a plan and timeline for remediation. On July 26, 2023, the TSA issued Security Directive Pipeline-2021-02D (Security Directive 2D), which requires owners/operators of critical pipelines to (1) establish and implement a TSA-approved Cybersecurity Implementation Plan that describes the specific cybersecurity measures employed and the schedule for achieving the cybersecurity outcomes described in Security Directive 2D; (2) develop and maintain a Cybersecurity Incident Response Plan to reduce the risk of operational disruption or other significant impacts from a cybersecurity incident; and (3) establish a Cybersecurity Assessment Program and submit an annual plan describing how the effectiveness of cybersecurity measures will be assessed. We have established and received TSA approval for our Cybersecurity Implementation Plan and are compliant with the remaining requirements established in Security Directives 1C and 2D. New regulations or security directives issued by TSA may impose additional requirements applicable to our cybersecurity program, which could cause us to incur increased capital and operating costs and operational delays. See “Risk Factors – A breach of our information technology infrastructure, including a breach caused by a cybersecurity attack on us or third parties with whom we are interconnected, may interfere with the safe operation of our assets, result in the disclosure of personal or proprietary information, and harm our reputation.”

EMPLOYEES

Northwest has no employees. Operations, management, and certain administrative services are provided by Williams and its affiliates.

TRANSACTIONS WITH AFFILIATES

We engage in transactions with Williams and other Williams’ subsidiaries. Please see Part II, Item 8. Financial Statements and Supplementary Data — Note 1 – Summary of Significant Accounting Policies and Note 9 – Transactions with Major Customers and Affiliates of Notes to Financial Statements.

Item 1A. Risk Factors

FORWARD-LOOKING STATEMENTS

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The reports, filings, and other public announcements of Northwest, may contain or incorporate by reference statements that do not directly or exclusively relate to historical facts. Such statements are “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. These forward-looking statements relate to anticipated financial performance, management’s plans and objectives for future operations, business prospects, outcome of regulatory proceedings, market conditions, and other matters.

All statements, other than statements of historical facts, included in this report that address activities, events, or developments that we expect, believe, or anticipate will exist or may occur in the future, are forward-looking statements. Forward-looking statements can be identified by various forms of words such as “anticipates,” “believes,” “seeks,” “could,” “may,” “should,” “continues,” “estimates,” “expects,” “forecasts,” “intends,” “might,” “goals,” “objectives,” “targets,” “planned,” “potential,” “projects,” “scheduled,” “will,” “assumes,” “guidance,” “outlook,” “in-service date,” or other similar expressions. These forward-looking statements are based on management’s beliefs and assumptions and on information currently available to management and include, among others, statements regarding:

•Our and our affiliates’ future credit ratings;

•Amounts and nature of future capital expenditures;

•Expansion and growth of our business and operations;

•Expected in-service dates for capital projects;

•Financial condition and liquidity;

•Business strategy;

•Cash flow from operations or results of operations;

•Rate case filings;

•Natural gas prices, supply, and demand; and

•Demand for our services.

Forward-looking statements are based on numerous assumptions, uncertainties, and risks that could cause future events or results to be materially different from those stated or implied in this report. Many of the factors that will determine these results are beyond our ability to control or predict. Specific factors that could cause actual results to differ from results contemplated by the forward-looking statements include, among others, the following:

•The impact of operational and developmental hazards and unforeseen interruptions;

•Development and rate of adoption of alternative energy sources;

•The strength and financial resources of our competitors and the effects of competition;

•Availability of supplies, including lower than anticipated volumes from third parties, and market demand;

•Volatility of pricing including the effect of lower than anticipated energy commodity prices;

•Changes in maintenance and construction costs, as well as our ability to obtain sufficient construction-related inputs, including skilled labor;

•The impact of existing and future laws and regulations, the regulatory environment, environmental matters, and litigation, as well as our ability and the ability of other energy companies, with whom we conduct or seek to conduct business, to obtain necessary permits and approvals, and our ability to achieve favorable rate proceeding outcomes;

•Increasing scrutiny and changing expectations from stakeholders with respect to our environmental, social, and governance practices;

•The physical and financial risks associated with climate change;

•Our exposure to the credit risk of our customers and counterparties;

•Our ability to successfully expand our facilities and operations;

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•Whether we are able to successfully identify, evaluate, and timely execute our capital projects and investment opportunities;

•Risks related to financing, including restrictions stemming from debt agreements, future changes in credit ratings as determined by nationally recognized credit rating agencies, and the availability and cost of capital;

•Inflation, interest rates, and general economic conditions (including future disruptions and volatility in the global credit markets and the impact of these events on customers and suppliers);

•Our costs for defined benefit pension plans and other postretirement benefit plans sponsored by our affiliates;

•The risks resulting from outbreaks or other public health crises;

•Changes in the current geopolitical situation, including the Russian invasion of Ukraine and conflicts in the Middle East including between Israel and Hamas and conflicts involving Iran and its proxy forces;

•Changes in U.S. governmental administration and policies;

•Risks associated with weather and natural phenomena, including climate conditions and physical damage to our facilities;

•Acts of terrorism, cybersecurity incidents, and related disruptions; and

•Additional risks described in our filings with the SEC.

Given the uncertainties and risk factors that could cause our actual results to differ materially from those contained in any forward-looking statement, we caution investors not to unduly rely on our forward-looking statements. We disclaim any obligations to and do not intend to update the above list or announce publicly the result of any revisions to any of the forward-looking statements to reflect future events or developments.

In addition to causing our actual results to differ, the factors listed above and referred to below may cause our intentions to change from those statements of intention set forth in this report. Such changes in our intentions may also cause our results to differ. We may change our intentions, at any time and without notice, based upon changes in such factors, our assumptions, or otherwise.

Because forward-looking statements involve risks and uncertainties, we caution that there are important factors, in addition to those listed above, that may cause actual results to differ materially from those contained in the forward-looking statements. These factors are described in the following section.

RISK FACTORS

You should carefully consider the following risk factors in addition to the other information in this report. If any of the risks discussed below occur, our business, prospects, financial condition, results of operations, cash flows and, in some cases our reputation, could be materially adversely affected. Each of these factors could adversely affect our business, operating results, and financial condition as well as adversely affect the value of an investment in our securities.

Risks Inherent to Our Industry and Business

Our natural gas transportation and storage activities involve numerous risks and hazards that might result in accidents and unforeseen interruptions.

Our operations are subject to all the risks and hazards typically associated with the transportation and storage of natural gas including, but not limited to:

•Aging infrastructure and mechanical problems;

•Damages to pipelines and pipeline blockages or other pipeline interruptions;

•Uncontrolled releases of natural gas;

•Operator error;

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•Damage caused by third party activity, such as operation of construction equipment;

•Pollution and other environmental risks;

•Fires, blowouts, cratering, and explosions; and

•Security risks, including cybersecurity.

Any of these risks could result in loss of human life, personal injuries, significant damage to property, environmental pollution, impairment of our operations, loss of services to our customers, reputational damage, and substantial losses to us. The location of certain segments of our pipeline in or near populated areas, including residential areas, commercial business centers, and industrial sites, could increase the level of damages resulting from these risks. An event such as those described above could cause considerable harm and have a material adverse effect on our financial condition and results of operations, particularly if the event is not fully covered by insurance.

Certain of our services are subject to long-term, fixed-price contracts that are not subject to adjustment, even if our cost to perform such services exceeds the revenues received from such contracts.

We provide some services pursuant to long-term, fixed-price contracts. It is possible that costs to perform services under such contracts will exceed the revenues we collect for our services. Although other services are priced at cost-based rates that are subject to adjustment in rate cases, under FERC policy, a regulated service provider and a customer may mutually agree to sign a contract for service at a “negotiated rate” that may be above or below the FERC regulated cost-based rate for that service. These “negotiated rate” contracts are not generally subject to adjustment for increased costs that could be produced by inflation or other factors relating to the specific facilities being used to perform the services.

We may not be able to extend or replace expiring natural gas transportation and storage contracts at favorable rates, on a long-term basis, or at all.

Our primary exposure to market risk occurs at the time the terms of existing transportation and storage contracts expire or are subject to termination. Upon expiration or termination of our existing contracts, we may not be able to extend such contracts with existing customers or obtain replacement contracts at favorable rates, on a long-term basis or at all. Failure to extend or replace a significant portion of our existing contracts may have a material adverse effect on our business, financial condition, results of operations, and cash flows. Our ability to extend or replace existing customer contracts on favorable terms is subject to a number of factors, some of which are beyond our control, including:

•The level of existing and new competition to deliver natural gas to our markets and competition from alternative fuel sources such as electricity, renewable resources, coal, fuel oils, or nuclear energy;

•Pricing, demand, availability, and margins for natural gas in our markets;

•Whether the market will continue to support long-term firm contracts;

•The effects of regulation on us, our customers, and our contracting practices; and

•The ability to understand our customers’ expectations, efficiently and reliably deliver high quality services, and effectively manage customer relationships. The results of these efforts will impact our reputation and positioning in the market.

Competitive pressures could lead to decreases in the volume of natural gas contracted for or transported through our pipeline system.

The principal elements of competition among natural gas transportation and storage assets are rates, terms of service, access to natural gas supplies, flexibility, and reliability. Although most of our pipeline system’s current capacity is fully contracted, the FERC has taken certain actions to strengthen market forces in the interstate natural gas pipeline industry that have led to increased competition throughout the industry. Similarly, a highly liquid competitive commodity market in natural gas and increasingly competitive markets for natural gas services, including competitive secondary markets in pipeline capacity, have developed. As a result, pipeline capacity is being used more efficiently, and peaking and storage services are increasingly effective substitutes for annual pipeline capacity. As a result, we could experience some “turnback” of firm capacity as the primary terms of existing agreements expire. If we are unable to remarket this capacity or can remarket it only at substantially

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discounted rates compared to previous contracts, we or our remaining customers may have to bear the costs associated with the turned back capacity.

We compete primarily with other interstate pipelines and storage facilities in the transportation and storage of natural gas. Some of our competitors may have greater financial resources and access to greater supplies of natural gas than we do. Some of these competitors may expand or construct transportation and storage systems that would create additional competition for natural gas supplies or the services we provide to our customers. Moreover, Williams and its other affiliates may not be limited in their ability to compete with us. In a number of key markets, interstate pipelines are now facing competitive pressure from other major pipeline systems, enabling local distribution companies and end users to choose a transmission provider based on considerations other than location. Other entities could construct new pipelines or expand existing pipelines that could potentially serve the same markets as our pipeline system. Any such new pipelines could offer transportation services that are more desirable to shippers because of locations, facilities, or other factors. These new pipelines could charge rates or provide service to locations that would result in greater net profit for shippers and producers and thereby force us to lower the rates charged for service on our pipeline in order to extend our existing transportation service agreements or to attract new customers. We are aware of proposals by competitors to expand pipeline capacity in certain markets we also serve which, if the proposed projects proceed, could increase the competitive pressure upon us. Further, natural gas also competes with other forms of energy available to our customers, including electricity, coal, fuel oils, and other alternative energy sources. We may not be able to successfully compete against current and future competitors and any failure to do so could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

Any significant decrease in supplies of natural gas in the supply basins we access or in demand for those supplies in the markets we serve could adversely affect our business and operating results.

Our ability to maintain and expand our business depends on the level of drilling and production predominately by third parties in our supply basins. Production from existing wells and natural gas supply basins with access to our pipeline will naturally decline over time. The amount of natural gas reserves underlying these existing wells may also be less than anticipated, and the rate at which production from these reserves declines may be greater than anticipated. We do not obtain independent evaluations of natural gas reserves underlying such wells and supply basins with access to our pipeline. Accordingly, we do not have independent estimates of total reserves dedicated to our pipeline or the anticipated life of such reserves. In addition, low prices for natural gas, regulatory limitations, including permitting and environmental regulations, or the lack of available capital for these projects could adversely affect the development and production of additional reserves, as well as gathering, storage, pipeline transportation, and import and export of natural gas supplies. Localized low natural gas prices in one or more of our existing supply basins, whether caused by a lack of infrastructure or otherwise, could also result in depressed natural gas production in such basins and limit the supply of natural gas made available to us. The competition for natural gas supplies to serve other markets could also reduce the amount of natural gas supply for our customers.

Demand for our transportation services depends on the ability and willingness of shippers with access to our facilities to satisfy demand in the markets we serve by deliveries through our system. Any decrease in this demand could adversely affect our business. Demand for natural gas is also affected by weather, future industrial and economic conditions, fuel conservation measures, alternative fuel requirements, governmental regulation including governmentally imposed constraints such as prohibitions on natural gas hookups in newly constructed buildings, and technological advances in fuel economy and energy generation devices, all of which are matters beyond our control.

A failure to obtain sufficient natural gas supplies or a reduction in demand for our services in the markets we serve could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

Significant prolonged changes in natural gas prices could affect supply and demand and cause a reduction in or termination of our long-term transportation and storage contracts or throughput on our system.

Higher natural gas prices over the long term could result in a decline in the demand for natural gas and, therefore, in our long-term transportation and storage contracts or throughput on our system. Also, lower natural gas prices over the long term could result in a decline in the production of natural gas, resulting in reduced contracts or throughput on our system. As a result, significant prolonged changes in natural gas prices could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

Our costs of testing, maintaining, or repairing our facilities may exceed our expectations, and the FERC may not allow, or competition in our markets may prevent, our recovery of such costs in the rates we charge for our services.

We have experienced and could experience in the future unexpected leaks or ruptures on our gas pipeline system or storage facilities. Either as a preventative measure or in response to a leak or another issue, we could be required by regulatory authorities to test or undertake modifications to our systems. If the cost of testing, maintaining, or repairing our facilities exceed

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expectations and the FERC does not allow us to recover, or competition in our markets prevents us from recovering, such costs in the rates that we charge for our services, such costs could have a material adverse impact on our business, financial condition, results of operations, and cash flows.

The operation of our businesses might be adversely affected by regulatory proceedings, changes in government regulations or in their interpretation or implementation, or the introduction of new laws or regulations applicable to our businesses or our customers.

Public and regulatory scrutiny of the energy industry has resulted in the proposal and/or implementation of increased regulations. Such scrutiny has also resulted in various inquiries, investigations, and court proceedings, including litigation of energy industry matters. Both the customers on our system and regulators have rights to challenge the rates we charge under certain circumstances. Any successful challenge could materially affect our results of operations.

Certain inquiries, investigations, and court proceedings are ongoing. Adverse effects may continue as a result of the uncertainty of these ongoing inquiries, investigations, and court proceedings, or additional inquiries and proceedings by federal or state regulatory agencies or private plaintiffs. In addition, we cannot predict the outcome of any of these inquiries or whether these inquiries will lead to additional legal proceedings against us, civil or criminal fines and/or penalties, or other regulatory action, including legislation, which might be materially adverse to the operation of our business and our revenues and net income or increase our operating costs in other ways. Current legal proceedings or other matters, including environmental matters, suits, regulatory appeals, and similar matters, might result in adverse decisions against us which, among other outcomes, could result in the imposition of substantial penalties and fines and could damage our reputation. The result of such adverse decisions, either individually or in the aggregate, could be material and may not be covered fully or at all by insurance.

In addition, existing regulations, including those pertaining to financial assurances to be provided by our businesses in respect of potential asset decommissioning and abandonment activities, might be revised, reinterpreted, or otherwise enforced in a manner that differs from prior regulatory action. New laws and regulations might also be adopted or become applicable to us, our customers, or our business activities. The current U.S. governmental administration and its policies, which often oppose the development or expansion of fossil fuel energy, have increased the likelihood of such legal and regulatory developments. If new laws or regulations are imposed relating to oil and gas extraction, or if additional or revised levels of reporting, regulation, or permitting moratoria are required or imposed, including those related to hydraulic fracturing, the volumes of natural gas that we transport could decline, our compliance costs could increase, and our results of operations could be adversely affected.

Increasing scrutiny and changing expectations from stakeholders with respect to our environmental, social and governance practices may impose additional costs on us or expose us to new or additional risks.

Companies across all industries are facing increasing scrutiny from stakeholders related to their environmental, social, and governance (ESG) practices. Investor advocacy groups, institutional investors, investment funds, and other influential investors are also increasingly focused on ESG practices and in recent years have placed increasing importance on the implications and social cost of their investments. Regardless of the industry, investors’ increased focus and activism related to ESG (as proponents or opponents) and similar matters may hinder access to capital, as investors may decide to reallocate capital or to not commit capital as a result of their assessment of a company’s ESG practices. Companies that do not adapt to or comply with investor or other stakeholder expectations and standards, which are evolving, or that are perceived to have not responded appropriately to the growing concern for ESG issues, regardless of whether there is a legal requirement to do so, may suffer from reputational damage and the business, financial condition, and/or stock price of such a company could be materially and adversely affected.

We face pressures from our stakeholders, who are increasingly focused on climate change, to prioritize sustainable energy practices, reduce our carbon footprint and promote sustainability. Our stakeholders may require us to implement ESG procedures or standards in order to continue engaging with us, to remain invested in us, or before they will make further investments in us. Additionally, we may face reputational challenges in the event our ESG procedures or standards do not meet the standards set by certain constituencies. We adopted certain practices as highlighted in Williams’ 2022 Sustainability Report, including with respect to air emissions, biodiversity and land use, climate change, and environmental stewardship. It is possible, however, that our stakeholders might not be satisfied with our sustainability efforts or the speed of their adoption. If we do not meet our stakeholders’ expectations, our business and/or our ability to access capital could be harmed.

Additionally, adverse effects upon the oil and gas industry related to the worldwide social and political environment, including uncertainty or instability resulting from climate change, changes in political leadership and environmental policies, changes in geopolitical-social views toward fossil fuels and renewable energy, concern about the environmental impact of climate change, and investors’ expectations regarding ESG matters, may also adversely affect demand for our services. Any long-term material adverse effect on the oil and gas industry could have a significant financial and operational adverse impact on our business.

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The occurrence of any of the foregoing could have a material adverse effect on our business and financial condition.

We may be subject to physical and financial risks associated with climate change.

The threat of global climate change may create physical and financial risks to our business. Energy needs vary with weather conditions. To the extent weather conditions may be affected by climate change, energy use could increase or decrease depending on the duration and magnitude of any changes. Increased energy use due to weather changes may require us to invest in more pipelines and other infrastructure to serve increased demand. A decrease in energy use due to weather changes may affect our financial condition through decreased revenues. Extreme weather conditions in general require more system backup, adding to costs, and can contribute to increased system stresses, including service interruptions. Weather conditions outside of our operating territory could also have an impact on our revenues. To the extent the frequency of extreme weather events increases, this could increase our cost of providing service. We may not be able to pass on the higher costs to our customers or recover all costs related to mitigating these physical risks.

Additionally, many climate models indicate that global warming is likely to result in rising sea levels and increased frequency and severity of weather events, which may lead to higher insurance costs, or a decrease in available coverage, for our assets in areas subject to severe weather. These climate-related changes could damage our physical assets, especially operations located in low-lying areas near river banks, and facilities situated in rain-susceptible regions.

To the extent financial markets view climate change and GHG emissions as a financial risk, this could negatively impact our cost of and access to capital. Climate change and GHG regulation could also reduce demand for our services. Our business could also be affected by the potential for lawsuits against GHG emitters, based on links drawn between GHG emissions and climate change.

Our operations are subject to environmental laws and regulations, including laws and regulations relating to climate change and greenhouse gas emissions, which may expose us to significant costs, liabilities, and expenditures that could exceed our expectations.

Our operations are subject to extensive federal, state, and local laws and regulations governing environmental protection, endangered and threatened species, the discharge of materials into the environment, and the security of chemical and industrial facilities. Substantial costs, liabilities, delays, and other significant issues related to environmental laws and regulations are inherent in the gathering, transportation, and storage of natural gas as well as waste disposal practices and construction activities. New or amended environmental laws and regulations can also result in significant increases in capital costs we incur to comply with such laws and regulations. Failure to comply with these laws, regulations, and permits may result in the assessment of administrative, civil, and/or criminal penalties, the imposition of remedial obligations, the imposition of stricter conditions on or revocation of permits, the issuance of injunctions limiting or preventing some or all of our operations, and delays or denials in granting permits.

Joint and several strict liability may be incurred without regard to fault under certain environmental laws and regulations for the remediation of contaminated areas and in connection with spills or releases of materials associated with natural gas, oil, and wastes on, under, or from our properties and facilities. Private parties, including the owners of properties through which our pipeline system passes and facilities where our wastes are taken for reclamation or disposal, may have the right to pursue legal actions to enforce compliance as well as to seek damages for noncompliance with environmental laws and regulations or for personal injury or property damage arising from our operations. Some sites at which we operate are located near current or former third-party hydrocarbon storage and processing or oil and natural gas operations or facilities, and there is a risk that contamination has migrated from those sites to ours.

We are generally responsible for all liabilities associated with the environmental condition of our facilities and assets, whether acquired or developed, regardless of when the liabilities arose and whether they are known or unknown. In connection with certain acquisitions and divestitures, we could acquire, or be required to provide indemnification against, environmental liabilities that could expose us to material losses, which may not be covered by insurance. In addition, the steps we could be required to take to bring certain facilities into compliance could be prohibitively expensive, and we might be required to shut down, divest, or alter the operation of those facilities, which might cause us to incur losses.

In addition, climate change regulations and the costs that may be associated with such regulations and with the regulation of emissions of GHGs have the potential to affect our business. Regulatory actions by the U.S. Environmental Protection Agency or the passage of new climate change laws or regulations could result in increased costs to operate and maintain our facilities, install new emissions controls on our facilities, or administer and manage any GHG emissions program. We believe it is possible that future governmental legislation and/or regulation may require us either to limit GHG emissions associated with our operations or to purchase allowances for such emissions. However, we cannot predict precisely what form these future regulations might take, the stringency of any such regulations or when they might become effective. Several legislative bills

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have been introduced in the United States Congress that would require carbon dioxide emission reductions. Previously considered proposals have included, among other things, limitations on the amount of GHGs that can be emitted (so called “caps”) together with systems of permitted emissions allowances. These proposals could require us to reduce emissions or to purchase allowances for such emissions.

In addition to activities on the federal level, state and regional initiatives could also lead to the regulation of GHG emissions sooner than and/or independent of federal regulation. These regulations could be more stringent than any federal legislation that may be adopted. Future legislation and/or regulation designed to reduce GHG emissions could make some of our activities uneconomic to maintain or operate. We continue to monitor legislative and regulatory developments in this area and otherwise take efforts to limit and reduce GHG emissions from our facilities. Although the regulation of GHG emissions may have a material impact on our operations and rates, we believe it is premature to attempt to quantify the potential costs of the impacts.

If we are unable to recover or pass through a significant level of our costs related to complying with climate change regulatory requirements imposed on us, it could have a material adverse effect on our results of operations and financial condition.

We depend on certain key customers for a significant portion of our revenues. The loss of any of these key customers or the loss of any contracted volumes could result in a decline in our business.

We rely on a limited number of customers for a significant portion of our revenues. Although some of these customers are subject to long-term contracts, we may be unable to negotiate extensions or replacements of these contracts on favorable terms, or at all. For the year ended December 31, 2023, our largest customer was Puget Sound Energy, Inc., which accounted for approximately 29 percent of our operating revenues. The loss of all, or even a portion of, the revenues from contracted volumes supplied by our key customers, as a result of competition, creditworthiness, inability to negotiate extensions or replacements of contracts, or otherwise, could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

We are exposed to the credit risk of our customers and counterparties and our credit risk management will not be able to completely eliminate such risk.

We are subject to the risk of loss resulting from nonpayment and/or nonperformance by our customers and counterparties in the ordinary course of our business. Generally, our customers are rated investment grade, are otherwise considered creditworthy, are required to make pre-payments or provide security to satisfy credit concerns, or are dependent upon us, in some cases without a readily available alternative, to provide necessary services. However, our credit procedures and policies cannot completely eliminate customer credit risk. Our customers and counterparties include industrial customers, local distribution companies, natural gas producers, and marketers whose creditworthiness may be suddenly and disparately impacted by, among other factors, commodity price volatility, deteriorating energy market conditions, and public and regulatory opposition to energy producing activities. In a low commodity price environment certain of our customers have been or could be negatively impacted, causing them significant economic stress resulting, in some cases, in a customer bankruptcy filing or an effort to renegotiate our contracts. To the extent one or more of our key customers commences bankruptcy proceedings, our contracts with such customers may be subject to rejection under applicable provisions of the United States Bankruptcy Code, or, if we so agree, may be renegotiated. Further, during any such bankruptcy proceeding, prior to assumption, rejection, or renegotiation of such contracts, the bankruptcy court may temporarily authorize the payment of value for our services less than contractually required, which could have a material adverse effect on our business, results of operations, cash flows, and financial condition. If we fail to adequately assess the creditworthiness of existing or future customers and counterparties, or otherwise do not take sufficient mitigating actions, including obtaining sufficient collateral, deterioration in their creditworthiness, and any resulting increase in nonpayment and/or nonperformance by them could cause us to write down or write off accounts receivable. Such write-downs or write-offs could negatively affect our operating results for the period in which they occur, and, if significant, could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

If third-party pipelines and other facilities interconnected to our pipeline and facilities become unavailable to transport natural gas, our revenues could be adversely affected.

We depend upon third-party pipelines and other facilities that provide delivery options to and from our pipeline and storage facilities for the benefit of our customers. Because we do not own these third-party pipelines or facilities, their continuing operation is not within our control. If these pipelines or other facilities were to become temporarily or permanently unavailable for any reason, or if throughput were reduced because of testing, line repair, damage to pipelines or facilities, reduced operating pressures, lack of capacity, increased credit requirements or rates charged by such pipelines or facilities, or other causes, we and our customers would have reduced capacity to transport, store or deliver natural gas to end use markets, thereby reducing our

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revenues. Any temporary or permanent interruption at any key pipeline interconnection causing a material reduction in volumes transported on our pipeline or stored at our facilities could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

We do not own all of the land on which our pipeline and facilities are located, which could disrupt our operations.

We do not own all of the land on which our pipeline and facilities have been constructed. As such, we are subject to the possibility of increased costs to retain necessary land use. In those instances in which we do not own the land on which our facilities are located, we obtain the rights to construct and operate our facilities on land owned by third parties and governmental agencies for a specific period of time. Our loss of any of these rights, through our inability to renew right-of-way contracts or otherwise, could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

We face opposition to operation and expansion of our pipelines and facilities from various individuals and groups.

We have experienced, and we anticipate that we will continue to face, opposition to the operation and expansion of our pipelines and facilities from governmental officials, environmental groups, landowners, tribal groups, local groups, and other advocates. In some instances, we encounter opposition that disfavors hydrocarbon-based energy supplies regardless of practical implementation or financial considerations. Opposition to our operation and expansion can take many forms, including the delay or denial of required governmental permits, organized protests, attempts to block or sabotage our operations, intervention in regulatory or administrative proceedings involving our assets, or lawsuits or other actions designed to prevent, disrupt, or delay the operation or expansion of our assets and business. In addition, acts of sabotage or eco-terrorism could cause significant damage or injury to people, property, or the environment or lead to extended interruptions of our operations. Any such event that delays or prevents the expansion of our business, that interrupts the revenues generated by our operations, or which causes us to make significant expenditures not covered by insurance, could adversely affect our financial condition and results of operations.

We may not be able to grow or effectively manage our growth.

As part of our growth strategy, we engage in significant capital projects. We have a project lifecycle process and an investment evaluation process. These are processes we use to identify, evaluate, and execute on acquisition opportunities and capital projects. We may not always have sufficient and accurate information to identify and value potential opportunities and risks or our investment evaluation process may be incomplete or flawed. Our growth may also be dependent upon the construction of new natural gas gathering, transportation, compression, processing, or treating pipelines and facilities, as well as the expansion of existing facilities. Additional risks associated with construction may include the inability to obtain rights-of-way, skilled labor, equipment, materials, permits, and other required inputs in a timely manner such that projects are completed on time and the risk that construction cost overruns, including due to inflation, could cause total project costs to exceed budgeted costs. Additional risks associated with growing our business include, among others, that:

•Changing circumstances and deviations in variables could negatively impact our investment analysis, including our projections of revenues, earnings, and cash flow relating to potential investment targets, resulting in outcomes that are materially different than anticipated;

•We could be required to contribute additional capital to support acquired businesses or assets and we may assume liabilities that were not disclosed to us that exceed our estimates and for which contractual protections are either unavailable or prove inadequate;

•Acquisitions could disrupt our ongoing business, distract management, divert financial and operational resources from existing operations, and make it difficult to maintain our current business standards, controls, and procedures; and

•Acquisitions and capital projects may require substantial new capital, including the issuance of debt or equity, and we may not be able to access credit or capital markets or obtain acceptable terms.

If realized, any of these risks could have an adverse impact on our financial condition, results of operations, including the possible impairment of our assets, or cash flows.

Risks Related to Strategy and Financing

A downgrade of our credit ratings, which are determined outside of our control by independent third parties, could impact our liquidity, access to capital, and our costs of doing business.

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Downgrades of our credit ratings increase our cost of borrowing and could require us to provide collateral to our counterparties, negatively impacting our available liquidity. In addition, our ability to access capital markets could be limited by a downgrade of our credit ratings.

Credit rating agencies perform independent analysis when assigning credit ratings. The analysis includes a number of criteria such as business composition, market and operational risks, as well as various financial tests. Credit rating agencies continue to review the criteria for industry sectors and various debt ratings and may make changes to those criteria from time to time. Credit ratings are subject to revision or withdrawal at any time by the credit ratings agencies.

Our ability to obtain credit in the future could be affected by Williams’ credit ratings.

Substantially all of Williams’ operations are conducted through its subsidiaries. Williams’ cash flows are substantially derived from loans, dividends, and distributions paid to it by its subsidiaries. Due to our relationship with Williams, our ability to obtain credit will be affected by Williams’ credit ratings. If Williams were to experience a deterioration in its credit standing or financial condition, our access to capital and our ratings could be adversely affected. Any downgrading of a Williams credit rating could result in a downgrading of our credit rating. A downgrading of a Williams credit rating could limit our ability to obtain financing in the future upon favorable terms, if at all.

Restrictions in our debt agreements and the amount of our indebtedness may affect our future financial and operating flexibility.

Our total outstanding long-term debt (including current portion) as of December 31, 2023 was $581.2 million.

The agreements governing our indebtedness contain covenants that restrict our ability to incur certain liens to support indebtedness and our ability to merge or consolidate or sell all or substantially all of our assets. In addition, certain of our debt agreements contain various covenants that restrict or limit, among other things, our ability to make certain distributions during the continuation of an event of default, and to enter into certain affiliate transactions and certain restrictive agreements and to change the nature of our business. Certain of our debt agreements also contain, and those we enter into in the future may contain, financial covenants and other limitations with which we will need to comply. Williams’ debt agreements contain similar covenants with respect to Williams and its subsidiaries, including us.

Our debt service obligations and the covenants described above could have important consequences. For example, they could, among other things:

•Make it more difficult for us to satisfy our obligations with respect to our indebtedness, which could in turn result in an event of default on such indebtedness;

•Impair our ability to obtain additional financing in the future for working capital, capital expenditures, general limited liability company purposes, or other purposes;

•Diminish our ability to withstand a continued or future downturn in our business or the economy generally;

•Require us to dedicate a substantial portion of our cash flow from operations to debt service payments, thereby reducing the availability of cash for working capital, capital expenditures, general limited liability company purposes, or other purposes; and

•Limit our flexibility in planning for, or reacting to, changes in our business and the industry in which we operate, including by limiting our ability to expand or pursue our business activities and by preventing us from engaging in certain transactions that might otherwise be considered beneficial to us.

Our ability to comply with our debt covenants, to repay, extend, or refinance our existing debt obligations and to obtain future credit will depend primarily on our operating performance. Our ability to refinance existing debt obligations or obtain future credit will also depend upon the current conditions in the credit markets and the availability of credit generally. If we are unable to comply with these covenants, meet our debt service obligations, or obtain future credit on favorable terms, or at all, we could be forced to restructure or refinance our indebtedness, seek additional equity capital, or sell assets. We may be unable to obtain financing or sell assets on satisfactory terms, or at all.

Our failure to comply with the covenants in the documents governing our indebtedness could result in events of default, which could render such indebtedness due and payable. We may not have sufficient liquidity to repay our indebtedness in such circumstances. In addition, cross-default or cross-acceleration provisions in our debt agreements could cause a default or acceleration to have a wider impact on our liquidity than might otherwise arise from a default or acceleration of a single debt

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instrument. For more information regarding our debt agreements, please read Part II, Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations — Capital Resources and Liquidity and Part II, Item 8. Financial Statements and Supplementary Data — Note 6 – Debt and Financing Arrangements of Notes to Financial Statements.

Difficult conditions in the global financial markets and the economy in general could negatively affect our business and results of operations.

Our business may be negatively impacted by adverse economic conditions or future disruptions in the global financial markets. Included among these potential negative impacts are industrial or economic contraction leading to reduced energy demand and lower prices for our products and services and increased difficulty in collecting amounts owed to us by our customers. Geopolitical tensions and conflicts including those in the Middle East between Israel and Hamas and Iran or its proxy forces, as well as the ongoing Russian invasion of Ukraine and the actions undertaken by western nations in response to these conflicts have had, and may continue to have, adverse impacts on global financial markets. We, along with Williams and Transcontinental Gas Pipe Line Company, LLC (Transco), are party to a credit agreement with aggregate commitments available of $3.75 billion, with up to an additional $500 million increase in aggregate commitments available under certain circumstances. We and Transco are each subject to a $500 million borrowing sublimit. As of December 31, 2023, we had a borrowing capacity of $500 million under such credit facility, but our ability to borrow under that facility could be impaired if one or more of our lenders fails to honor its contractual obligation to lend to us. If financing is not available when needed, or is available only on unfavorable terms, we may be unable to implement our business plans or otherwise take advantage of business opportunities or respond to competitive pressures. In addition, financial markets have periodically been affected by concerns over U.S. fiscal and monetary policies. These concerns, as well as actions taken by the U.S. federal government in response to these concerns, could significantly and adversely impact the global and U.S. economies and financial markets, which could negatively impact us in the manner described above.

Williams can exercise substantial control over our distribution policy and our business and operations and may do so in a manner that is adverse to our interests.

Because we are an indirect wholly-owned subsidiary of Williams, Williams exercises substantial control over our business and operations and makes determinations with respect to, among other things, the following:

•Payment of distributions and repayment of advances;

•Decisions on financings and our capital raising activities;

•Mergers or other business combinations; and

•Acquisition or disposition of assets.

Williams could decide to increase distributions or advances to our member consistent with existing debt covenants. This could adversely affect our liquidity.

Risks Related to Regulations That Affect Our Industry

Our natural gas transportation and storage operations are subject to regulation by the FERC, which could have an adverse impact on our ability to establish transportation and storage rates that would allow us to recover the full cost of operating our pipeline and storage assets, including a reasonable rate of return.

In addition to regulation by other federal, state, and local regulatory authorities, under the NGA, our interstate pipeline transportation and storage services and related assets are subject to regulation by the FERC. Federal regulation extends to such matters as:

•Transportation of natural gas in interstate commerce;

•Rates, operating terms, types of services and conditions of service;

•Certification and construction of new interstate pipeline and storage facilities;

•Acquisition, extension, disposition, or abandonment of existing interstate pipeline and storage facilities;

•Accounts and records;

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•Depreciation and amortization policies;

•Relationships with affiliated companies that are involved in marketing functions of the natural gas business; and

•Market manipulation in connection with interstate sales, purchases, or transportation of natural gas.

Regulatory or administrative actions in these areas, including successful complaints or protests against our rates, can affect our business in many ways, including by decreasing existing tariff rates or setting future tariff rates to levels such that revenues are inadequate to recover increases in operating costs or to sustain an adequate return on capital investments, decreasing volumes in our pipelines, increasing our costs, and otherwise altering the profitability of our business.

Risks Related to Employees and Outsourcing of Support Activities

Failure of our service providers or disruptions to outsourcing relationships might negatively impact our ability to conduct our business.

We rely on Williams and other third parties for certain services necessary for us to be able to conduct our business. We have a limited ability to control these operations and the associated costs. Certain of Williams’ accounting and information technology functions that we rely on are currently provided by third-party vendors, and sometimes from service centers outside of the United States. Services provided pursuant to these arrangements could be disrupted. Similarly, the expiration of agreements associated with such arrangements or the transition of services between providers could lead to loss of institutional knowledge or service disruptions. Our reliance on Williams and others as service providers and on Williams’ outsourcing relationships, and our limited ability to control certain costs, could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

Our allocation from Williams for costs for its defined benefit pension plans and other postretirement benefit plans are affected by factors beyond our and Williams’ control.

As we have no employees, employees of Williams and its affiliates provide services to us. As a result, we are allocated a portion of Williams’ costs for defined benefit pension plans and other postretirement benefit plans. The timing and amount of our allocations under the defined benefit pension plans depend upon a number of factors that Williams controls, including changes to pension plan benefits, as well as factors outside of Williams’ control, such as asset returns, interest rates, and changes in pension laws. Changes to these and other factors that can significantly increase our allocations could have a significant adverse effect on our results of operations and financial condition.

Risks Related to Weather, Other Natural Phenomena and Business Disruption

Our assets and operations, as well as our customers’ assets and operations, can be affected by weather and other natural phenomena.

Our assets and operations and our customers’ assets and operations can be adversely affected by hurricanes, floods, earthquakes, landslides, tornadoes, and other natural phenomena and weather conditions, including extreme or unseasonable temperatures, making it more difficult for us to realize the historic rates of return associated with our assets and operations. A significant disruption in our or our customers’ operations or the occurrence of a significant liability for which we were not fully insured could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

Our business could be negatively impacted by acts of terrorism and related disruptions.

Given the volatile nature of the commodities we transport and store, our assets and the assets of our customers and others in our industry may be targets of terrorist activities. Uncertainty surrounding the Russian invasion of Ukraine, conflicts in the Middle East including between Israel and Hamas and conflicts involving Iran and its proxy forces, or other sustained military campaigns, may affect our operations in unpredictable ways, including the possibility that infrastructure facilities could be direct targets of, or indirect casualties of, an act of terrorism. A terrorist attack could create significant price volatility, disrupt our business, limit our access to capital markets, or cause significant harm to our operations, such as full or partial disruption to our ability to transport natural gas. Acts of terrorism, as well as events occurring in response to or in connection with acts of terrorism, could cause environmental repercussions that could result in a significant decrease in revenues or significant reconstruction or remediation costs, which could have a material adverse effect on our business, financial condition, results of operations, and cash flows.

A breach of our information technology infrastructure, including a breach caused by a cybersecurity attack on us or third parties with whom we are interconnected, may interfere with the safe operation of our assets, result in the disclosure of personal or proprietary information, and harm our reputation.

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We rely on our information technology infrastructure to process, transmit, and store electronic information, including information we use to safely operate our assets. In addition to the oversight of our business provided by our Management Committee, the Williams’ Board of Directors has oversight responsibility with regard to enterprise-wide assessment of the major risks inherent in its businesses, including cybersecurity risks. Accordingly, the Williams’ Board of Directors reviews management’s efforts to address and mitigate such risks, including the establishment and implementation of policies to address cybersecurity threats. We have invested, and expect to continue to invest, significant time, manpower, and capital in our information technology infrastructure. However, the age, operating systems, or condition of our current information technology infrastructure and software assets and our ability to maintain and upgrade such assets could affect our ability to resist cybersecurity threats. While we believe that we maintain appropriate information security policies, practices, and protocols, we regularly face cybersecurity and other security threats to our information technology infrastructure, which could include threats to our operational industrial control systems and safety systems that operate our pipelines, plants, and assets. We face unlawful attempts to gain access to our information technology infrastructure, including coordinated attacks from hackers, whether state-sponsored groups, “hacktivists”, or private individuals. We face the threat of theft and misuse of sensitive data and information, including customer and employee information. We also face attempts to gain access to information related to our assets through attempts to obtain unauthorized access by targeting acts of deception against individuals with legitimate access to physical locations or information. We also are subject to cybersecurity risks arising from the fact that our business operations are interconnected with third parties, including third-party pipelines, other facilities, and our contractors and vendors. In addition, the breach of certain business systems could affect our ability to correctly record, process, and report financial information. Breaches in our information technology infrastructure or physical facilities, or other disruptions, including those arising from theft, vandalism, fraud, or unethical conduct, which may increase as a result of the Russian invasion of Ukraine or other geopolitical tensions and conflicts, could result in damage to or destruction of our assets, unnecessary waste, safety incidents, damage to the environment, reputational damage, potential liability, the loss of contracts, the imposition of significant costs associated with remediation and litigation, heightened regulatory scrutiny, increased insurance costs, and have a material adverse effect on our operations, financial condition, results of operations, and cash flows.

General Risk Factors

We do not insure against all potential risks and losses and could be seriously harmed by unexpected liabilities or by the inability of our insurers to satisfy our claims.

In accordance with customary industry practice, we maintain insurance against some, but not all, risks and losses, and only at levels we believe to be appropriate. The occurrence of any risks not fully covered by insurance could have a material adverse effect on our business, financial condition, results of operations, and cash flows, and our ability to repay our debt.

A failure to attract and retain an appropriately qualified workforce could negatively impact our results of operations.

Events such as an aging workforce without appropriate replacements, mismatch of skill sets to future needs, or unavailability of contract labor may lead to operating challenges such as lack of resources, loss of knowledge, and a lengthy time period associated with skill development, including with the workforce needs associated with projects and ongoing operations. Williams’ failure to hire and adequately obtain replacement employees, including the ability to transfer significant internal historical knowledge and expertise to the new employees, or the future availability and cost of contract labor, may adversely affect our ability to manage and operate the businesses. If Williams is unable to successfully attract and retain an appropriately qualified workforce, including members of senior management, results of operations could be negatively impacted.

Item 1B. Unresolved Staff Comments

None.

Item 1C. Cybersecurity

We recognize the increasing volume and sophistication of cyber threats and take our responsibility to protect the information and systems under our purview seriously. Our cybersecurity processes aim to provide a comprehensive approach to assess, identify, and manage material risks arising from these cybersecurity threats.

Comprehensive Cybersecurity Program: We have implemented a comprehensive cybersecurity risk management program (Cybersecurity Program) that is aligned with the National Institute for Standards and Technology Cybersecurity Framework. Our Cybersecurity Program provides a risk-based approach to cybersecurity, and security controls are tailored so that cost-effective controls can be applied commensurate with the risk and sensitivity of specific information systems, control systems

18

and enterprise data. Our Cybersecurity Program incorporates best practices and industry standards from multiple sources and is designed to comply with applicable regulations. The Cybersecurity Program includes, but is not limited to, the following elements: risk assessment, policies and procedures, training and awareness, auditing, compliance monitoring and testing, and incident response.

Integration with Overall Risk Management: Our cybersecurity processes have been integrated into our overall risk management system and processes. We consider cybersecurity threat risks alongside other Company risks as part of our overall risk assessment process. Our cybersecurity risk professionals collaborate with subject matter specialists, as necessary, to gather insights for identifying and assessing material cybersecurity threat risks, their severity, and potential mitigations.

Engagement of Third Parties: We often engage with specialized third-party assessors, consultants, auditors, and other experts to review, validate, and enhance our cybersecurity practices. Their independent assessments provide an external perspective on our cybersecurity posture, allowing us to leverage best practices from the industry and ensure our defenses remain robust. All third parties engaged for such processes are subjected to rigorous scrutiny to ensure they meet our security standards, and the engagements are documented and reviewed periodically.

Oversight of Third-party Service Providers: We acknowledge the potential risks associated with our use of third-party service providers. Therefore, we have established processes to oversee and identify material cybersecurity risks that may be associated with third-party service providers with whom we engage. This includes conducting thorough, risk-based due diligence before onboarding, performing security assessments, and confirming adherence to our cybersecurity requirements. We also maintain active communication channels with these providers to stay informed about any potential security incidents or concerns.

Disclosure of Risks: We describe how risks from cybersecurity threats, could materially affect us, including our business strategy, results of operations, or financial condition, as part of our risk factor disclosures at Part I, Item 1A of this Annual Report on Form 10-K.

We are committed to continually enhancing our cybersecurity processes and practices to address the dynamic nature of the threats we face and to ensure the security and integrity of our systems and data.

Cybersecurity Governance

Cybersecurity is an important part of our risk management processes and an area of focus for Williams’ Board of Directors and management. Each member of our organization, from facility operators to board members, has a responsibility to safeguard our cybersecurity. Williams’ Chief Information Security Officer (CISO) is responsible for our cybersecurity strategy and execution, while the Board and Williams’ Audit Committee are responsible for oversight of our cybersecurity risk.

The Cybersecurity Executive Advisory Board (Executive Advisory Board) is led by the CISO, with Williams’ Chief Information Officer (CIO), Chief Financial Officer, Chief Human Resources Officer, General Counsel, and Chief Operations Officer as standing members. The Executive Advisory Board’s purpose is to ensure enterprise alignment with the Cybersecurity Program and provide executive oversight of the Cybersecurity Program.

The Williams’ Board of Directors oversees cybersecurity-related policy and strategy. As part of this oversight, the CISO provides a cybersecurity dashboard that is reviewed by the Board at every regularly scheduled Board meeting, which includes key performance indicators for cybersecurity process maturity, operational performance, and enterprise performance toward TSA compliance. Additionally, the CIO and/or CISO presents to the Board bi-annually regarding our cybersecurity risks and strategies, including as part of our annual long-term strategy session. The Audit Committee, comprised of independent directors, reviews the implementation and effectiveness of cybersecurity risk management protocols and reviews the effectiveness of cybersecurity as part of the Company’s accounting and internal control policies. As part of this oversight, the CIO presents to the Audit Committee bi-annually, as well as periodically in conjunction with any internal audits related to cybersecurity. Additionally, we have protocols by which cybersecurity incidents that meet established reporting thresholds are escalated internally and, where appropriate, are reported to the Board, as well as ongoing updates regarding any such incident until it has been addressed.

The CIO has been in his role at Williams for over 10 years and has over 30 years of combined Information Technology experience with a broad scope of responsibility. He has provided senior leadership support of the cybersecurity and risk management programs since 2013. Our CIO holds a bachelor’s degree in management information systems (MIS) from the University of Oklahoma and a Master of Business Administration in MIS from the University of Dallas.

The CISO has been at Williams for over 25 years. During that time, he has held a variety of IT positions at multiple levels in the organization ranging from network engineering to application development, project management as well as several IT Manager and Director roles. He has had oversight of our cybersecurity and risk management programs since 2017. Active in government and private sector partnerships, he is currently serving as the outgoing Chair of the Oil & Natural Gas Subsector Coordinating Council and recently acted as the Chair of the Interstate Natural Gas Association of America security committee.

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Our CISO holds degrees in Business Administration and MIS from the University of Oklahoma and is certified in Leadership from Harvard Business School’s executive education. In 2018, he obtained his Chief Information Security Officer certification from Carnegie Mellon University.

Item 2. Properties

Our gas pipeline facilities are generally owned in fee simple. However, a substantial portion of such facilities is constructed and maintained on and across properties owned by others pursuant to rights-of-way, easements, permits, licenses or consents. Our compressor stations, with associated facilities, are located in whole or in part upon lands owned by us and upon sites held under leases or permits issued or approved by public authorities. Land owned by others, but used by us under rights-of-way, easements, permits, leases, licenses, or consents, includes land owned by private parties, federal, state, and local governments, quasi-governmental agencies, or Native American tribes. The Plymouth LNG facility is located on lands owned in fee simple by us. Various credit arrangements restrict the sale or disposal of a major portion of our pipeline system. We lease our company offices in Salt Lake City, Utah.

Item 3. Legal Proceedings

Environmental

While it is not possible for us to predict the final outcome of any pending legal proceedings involving governmental authorities under federal, state, and local laws regulating the discharge of materials into the environment, we do not anticipate a material effect on our financial position if we were to receive an unfavorable outcome in any one or more of such proceedings. Our threshold for disclosing material environmental legal proceedings involving a governmental authority where potential monetary sanctions are involved is $1 million.

Other

The additional information called for by this item is provided in Part II, Item 8. Financial Statements and Supplementary Data – Note 5 – Contingent Liabilities and Commitments of Notes to Financial Statements.

Item 4. Mine Safety Disclosures

Not applicable.

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PART II

Item 5. Market for Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities

We are indirectly owned by Williams.

Cash distributions totaling $154.8 million and $137.9 million were declared and paid by us to our parent during the years ended December 31, 2023 and 2022, respectively. In January 2024, we declared and paid cash distributions to our parent of $33.0 million.

Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations

General

The following discussion and analysis of critical accounting estimates, results of operations, and capital resources and liquidity should be read in conjunction with the financial statements and notes thereto included within Part II, Item 8 of this report.

Critical Accounting Estimates

The preparation of financial statements in conformity with generally accepted accounting principles requires management to make estimates and assumptions. We believe that the nature of these estimates and assumptions is material due to the subjectivity and judgment necessary, or the susceptibility of such matters to change, and the impact of these on our financial condition or results of operations.

Regulatory Accounting

We are regulated by the FERC. Accounting Standards Codification (ASC) Topic 980, “Regulated Operations,” (Topic 980) provides that certain costs that would otherwise be charged to expense should be deferred as regulatory assets, based on the expected recovery from customers in future rates. Likewise, certain actual or anticipated credits that would otherwise reduce expense should be deferred as regulatory liabilities, based on the expected return to customers in future rates. Management's expected recovery of deferred costs and return of deferred credits generally results from specific decisions by regulators granting such ratemaking treatment. We record certain incurred costs and obligations as regulatory assets or liabilities if, based on regulatory orders or other available evidence, it is probable that the costs or obligations will be included in amounts allowable for recovery or refunded in future rates.

Accounting for businesses that are regulated and apply the provisions of Topic 980 can differ from the accounting requirements for non-regulated businesses. Transactions that are recorded differently as a result of regulatory accounting requirements include the capitalization of an equity return component on regulated capital projects, capitalization of other project costs, retirements of general plant assets, levelized cost of service, negative salvage, asset retirement obligations (ARO), employee-related benefits, environmental costs, and other costs and taxes included in, or expected to be included in, future rates. As a rate-regulated entity, our management has determined that it is appropriate to apply the accounting prescribed by Topic 980 and, accordingly, the accompanying financial statements include the effects of the types of transactions described above that result from regulatory accounting requirements. Management’s assessment of the probability of recovery or pass through of regulatory assets and liabilities requires judgment and interpretation of laws and regulatory commission orders. If, for any reason, we cease to meet the criteria for application of regulatory accounting treatment for all or part of our operations, the regulatory assets and liabilities related to those portions ceasing to meet such criteria would be eliminated from the Balance Sheet and included in the Statement of Net Income for the period in which the discontinuance of regulatory accounting treatment occurs, unless otherwise required to be recorded under other provisions of U.S. generally accepted accounting principles. The aggregate amount of regulatory assets reflected on the Balance Sheet is $37.9 million at December 31, 2023. The aggregate amount of regulatory liabilities reflected on the Balance Sheet is $273.6 million at December 31, 2023. A summary of regulatory assets and liabilities is included in Note 11 – Regulatory Assets and Liabilities of Notes to Financial Statements.

Results of Operations

This analysis discusses financial results of our operations for the years 2023 and 2022. Variances due to changes in natural gas prices and transportation volumes have little impact on revenues, because under our rate design methodology, the majority of overall cost of service is recovered through firm capacity reservation charges in our transportation rates.

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Net Income for the year ended December 31, 2023 of $179.7 million increased $42.9 million, or 31 percent, when compared to the $136.8 million of net income for the year ended December 31, 2022 due to the following significant variances:

Operating Revenues decreased $7.5 million, or 2 percent, primarily driven by:

•$14.9 million decrease in Natural gas transportation revenues due to new rates that became effective January 1, 2023 as a result of the approval of our Settlement (also see Note 4 – Rate and Regulatory Matters), which was partially offset by higher short-term firm transportation;

•$5.2 million increase in Other revenues from higher park and loan services; and

•$2.2 million increase in Natural gas storage revenues due to an increase in storage rates effective January 1, 2023 as a result of our Settlement.

Operating Expenses decreased $43.0 million, or 15 percent, primarily due to:

•$19.6 million favorable change in Regulatory charges resulting from tax rate changes due to the absence of the accrual for refund related to the regulatory liability associated with Tax Reform that ended in 2022 and was refunded to customers in January 2023 (see Note 11 – Regulatory Assets and Liabilities); and

•$18.2 million favorable change in Other (income) expense, net primarily related to the amortization of our regulatory liabilities associated with deferred taxes that were established as a result of decreases in the estimated effective federal and state income tax rates.

Other (Income) and Other Expenses had a $7.5 million favorable change primarily due to an increase in interest income on our advances to Williams due to rising interest rates and the absence of interest expense on the regulatory liability associated with the decrease in federal tax rates due to Tax Reform that was refunded to customers in January 2023 as a result of the Settlement (also see Note 4 – Rate and Regulatory Matters).

Capital Resources and Liquidity

Method of Financing

We fund our capital requirements with cash flows from operating activities, equity contributions from Williams, advances from Williams, accessing capital markets, and, if required, borrowings under the credit facility described below.

We may raise capital through private debt offerings, as well as offerings registered pursuant to offering-specific registration statements. Interest rates, market conditions, and industry conditions will affect amounts raised, if any, in the capital markets. We anticipate that we will be able to access public and private debt markets on terms commensurate with our credit ratings to finance our capital requirements, when needed.

We, along with Williams and Transco, are co-borrowers under a $3.75 billion unsecured credit facility. Total letter of credit capacity available to Williams under the credit facility is $500 million. We may borrow up to $500 million under the credit facility to the extent not otherwise utilized by Williams and Transco. See Note 6 – Debt and Financing Arrangements of Notes to Financial Statements for further discussion of the credit facility.

We are a participant in Williams’ cash management program, and we make advances to and receive advances from Williams. At December 31, 2023, our advances to Williams totaled approximately $157.8 million. These advances are represented by demand notes. See Note 9 – Transactions with Major Customers and Affiliates of Notes to Financial Statements for further discussion.

Capital Expenditures

We categorize our capital expenditures as either maintenance capital expenditures or expansion capital expenditures. Maintenance capital expenditures are those expenditures required to maintain the existing operating capacity and service capability of our assets, including replacement of system components and equipment that are worn, obsolete, completing their useful life, or necessary to remain in compliance with environmental laws and regulations. Expansion capital expenditures improve the service capability of existing assets, extend useful lives, increase transmission or storage capacities from existing levels, reduce costs, or enhance revenues. We anticipate 2024 capital expenditures will be approximately $7 million for expansion projects and $232 million for maintenance projects. In 2024, we expect to fund our capital expenditures with cash from operations.

22

Item 7A. Quantitative and Qualitative Disclosures About Market Risk

Interest Rate Risk

At December 31, 2023, our debt portfolio included only fixed rate debt, which mitigates the impact of fluctuations in interest rates. The following table provides information about our long-term debt (in thousands of dollars):

	December 31, 2023
Fixed rates on long-term debt:
7.125% Debentures due 2025	$	85,000
4.0% Notes due 2027	500,000
	585,000
Unamortized debt issuance costs	(1,954)
Unamortized debt discount	(1,868)
Total long-term debt, including current portion	$	581,178

Our total long-term debt at December 31, 2023 had a carrying value of $581.2 million and a fair market value of $581.1 million. As of December 31, 2023, the weighted-average interest rate on our long-term debt was 4.45 percent.

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Item 8. Financial Statements and Supplementary Data

INDEX TO FINANCIAL STATEMENTS

	Page
Report of Independent Registered Public Accounting Firm (PCAOB ID: 42)	25
Statement of Net Income	27
Balance Sheet	28
Statement of Changes in Member's Equity	30
Statement of Cash Flows	31
Notes to Financial Statements	32
Note 1 – Summary of Significant Accounting Policies	32
Note 2 – Revenue Recognition	37
Note 3 – Leases	38
Note 4 – Rate and Regulatory Matters	39
Note 5 – Contingent Liabilities and Commitments	39
Note 6 – Debt and Financing Arrangements	41
Note 7 – Benefit Plans	42
Note 8 – Financial Instruments	43
Note 9 – Transactions with Major Customers and Affiliates	43
Note 10 – Asset Retirement Obligations	44
Note 11 – Regulatory Assets and Liabilities	45

24

Report of Independent Registered Public Accounting Firm

To the Management Committee and Member of Northwest Pipeline LLC

Opinion on the Financial Statements

We have audited the accompanying balance sheets of Northwest Pipeline LLC (the Company) as of December 31, 2023 and 2022, the related statements of net income, changes in member’s equity and cash flows for each of the three years in the period ended December 31, 2023, and the related notes (collectively referred to as the “financial statements”). In our opinion, the financial statements present fairly, in all material respects, the financial position of the Company at December 31, 2023 and 2022, and the results of its operations and its cash flows for each of the three years in the period ended December 31, 2023, in conformity with U.S. generally accepted accounting principles.

Basis for Opinion

These financial statements are the responsibility of the Company's management. Our responsibility is to express an opinion on the Company’s financial statements based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) (PCAOB) and are required to be independent with respect to the Company in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement, whether due to error or fraud. The Company is not required to have, nor were we engaged to perform, an audit of its internal control over financial reporting. As part of our audits we are required to obtain an understanding of internal control over financial reporting but not for the purpose of expressing an opinion on the effectiveness of the Company's internal control over financial reporting. Accordingly, we express no such opinion.

Our audits included performing procedures to assess the risks of material misstatement of the financial statements, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the financial statements. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the financial statements. We believe that our audits provide a reasonable basis for our opinion.

Critical Audit Matter

The critical audit matter communicated below is a matter arising from the current period audit of the financial statements that was communicated or required to be communicated to the audit committee and that: (1) relates to accounts or disclosures that are material to the financial statements and (2) involved our especially challenging, subjective or complex judgments. The communication of the critical audit matter does not alter in any way our opinion on the financial statements, taken as a whole, and we are not, by communicating the critical audit matter below, providing a separate opinion on the critical audit matter or on the accounts or disclosures to which it relates.

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Description of the Matter

Regulatory Assets and Liabilities As discussed in Note 1 to the financial statements, the Company is an interstate natural gas transmission company that is regulated by the Federal Energy Regulatory Commission (“FERC”) and applies accounting principles in Topic 980 for regulated operations. As such, certain incurred costs that would otherwise be charged to expense are deferred as regulatory assets, based on the expected recovery from customers in future rates. Likewise, certain actual or anticipated credits that would otherwise reduce expense are deferred as regulatory liabilities, based on the expected return to customers in future rates. The Company records items as regulatory assets or liabilities if, based on regulatory orders or other available evidence, it is probable that the costs or obligations will be included in amounts allowable for recovery or refunded in future rates. Auditing regulatory assets and liabilities is complex as it requires specialized knowledge of rate-regulated activities and judgments about matters that could affect the recording of regulatory assets and liabilities.

How We Addressed the Matter in Our Audit

We obtained an understanding, evaluated the design, and tested the operating effectiveness of internal controls over the Company’s accounting for regulatory assets and liabilities, including, among others, controls over the evaluation of filings with regulatory bodies and their effects on existing regulatory assets and liabilities, including factors that may affect the timing or nature of recoverability. We performed audit procedures that included, among others, reviewing evidence of correspondence with regulatory bodies to test that the Company evaluated information obtained from regulatory rulings. For example, we assessed the recoverability, considering information obtained from regulatory orders, of various regulatory assets. In addition, we tested calculations of material regulatory assets and liabilities, including that amortization for certain regulatory assets and liabilities corresponded to relevant regulatory filings and/or orders.

/s/ Ernst & Young LLP

We have served as the Company’s auditor since 1986.

Houston, Texas

February 21, 2024

26

Northwest Pipeline LLC

Statement of Net Income

	Year Ended December 31,
	2023		2022		2021
	(Thousands)
Operating Revenues:
Natural gas transportation	$	414,647	$	429,526	$	428,136
Natural gas storage	15,298		13,104		12,883
Other	9,913		4,705		2,539
Total operating revenues	439,858		447,335		443,558
Operating Expenses:
Operation and maintenance	88,005		84,260		76,016
General and administrative	50,524		51,682		49,204
Depreciation and amortization	111,434		114,384		113,180
Taxes, other than income taxes	12,297		17,039		16,836
Regulatory charges resulting from tax rate changes	—		19,621		23,580
Other (income) expense, net	(16,519)		1,712		1,449
Total operating expenses	245,741		288,698		280,265
Operating Income	194,117		158,637		163,293
Other (Income) and Other Expenses:
Interest expense	27,863		30,987		29,986
Allowance for equity and borrowed funds used during construction (AFUDC)	(3,846)		(2,950)		(1,606)
Miscellaneous other (income) expense, net	(9,619)		(6,174)		(595)
Total other (income) and other expenses	14,398		21,863		27,785
Net Income	$	179,719	$	136,774	$	135,508

See accompanying notes.

27

Northwest Pipeline LLC

Balance Sheet

	December 31,
	2023		2022
	(Thousands)
ASSETS
Current Assets:
Cash	$	—	$	—
Receivables:
Advances to affiliate	157,776		310,641
Trade	39,080		39,746
Affiliates	1,375		1,829
Other	1,485		606
Materials and supplies, at average cost	7,759		8,925
Exchange gas receivables	3,165		35,851
Regulatory assets	2,054		13,565
Other	1,801		3,627
Total current assets	214,495		414,790
Property, plant and equipment	3,974,900		3,836,254
Less-Accumulated depreciation and amortization	2,026,007		1,941,806
Total property, plant and equipment, net	1,948,893		1,894,448
Other Long-Term Assets:
Regulatory assets	35,796		15,951
Right-of-use assets	8,725		9,621
Deferred charges and other	19,450		15,167
Total other assets	63,971		40,739
Total assets	$	2,227,359	$	2,349,977

(continued)

See accompanying notes.

28

Northwest Pipeline LLC

Balance Sheet

	December 31,
	2023		2022
	(Thousands)
LIABILITIES AND MEMBER’S EQUITY
Current Liabilities:
Payables:
Trade	$	47,822	$	25,761
Affiliates	12,780		12,115
Accrued liabilities:
Exchange gas payables	5,553		42,451
Regulatory liabilities	21,374		145,243
Taxes, other than income taxes	7,388		10,853
Interest	5,505		5,505
Customer advances	5,016		4,415
Other	10,588		4,011
Total current liabilities	116,026		250,354
Long-Term Debt	581,178		580,083
Other Long-Term Liabilities:
Regulatory liabilities	252,272		271,706
Asset retirement obligations	136,263		129,306
Lease liability	7,193		7,857
Other	1,231		2,394
Total other long-term liabilities	396,959		411,263
Contingent Liabilities and Commitments (Note 5)
Member's Equity:
Member’s capital	1,073,892		1,073,892
Retained earnings	59,304		34,385
Total member’s equity	1,133,196		1,108,277
Total liabilities and member’s equity	$	2,227,359	$	2,349,977

See accompanying notes.

29

Northwest Pipeline LLC

Statement of Changes in Member’s Equity

	Year Ended December 31,
	2023		2022		2021
	(Thousands)
Member's Capital:
Balance at beginning and end of period	$	1,073,892	$	1,073,892	$	1,073,892
Retained Earnings:
Balance at beginning of period	34,385		35,511		66,503
Net income	179,719		136,774		135,508
Cash distributions to parent	(154,800)		(137,900)		(166,500)
Balance at end of period	59,304		34,385		35,511
Total Member’s Equity	$	1,133,196	$	1,108,277	$	1,109,403

See accompanying notes.

30

Northwest Pipeline LLC

Statement of Cash Flows

	Year Ended December 31,
	2023		2022		2021
	(Thousands)
OPERATING ACTIVITIES:
Net income	$	179,719	$	136,774	$	135,508
Adjustments to reconcile net cash provided (used) by operating activities:
Depreciation and amortization	111,434		114,384		113,180
Regulatory charges resulting from tax rate changes	—		19,621		23,580
Allowance for equity funds used during construction (equity AFUDC)	(3,155)		(2,335)		(1,360)
Changes in current assets and liabilities:
Trade and other accounts receivable	(213)		(515)		(1,632)
Affiliate receivables	454		(1,457)		(321)
Materials and supplies	1,166		(16)		898
Regulatory assets	(340)		(445)		111
Other current assets	1,432		(345)		(221)
Trade accounts payable	4,295		(1,230)		(3,571)
Affiliate payables	665		(1,025)		9,030
Regulatory liabilities	(125,502)		145,242		2
Other accrued liabilities	3,021		1,361		(877)
Other, including changes in long-term assets and liabilities:
Regulatory assets	(28,813)		—		—
Regulatory liabilities	(19,530)		(140,190)		4,374
Other, net	4,615		(1,182)		(5,739)
Net cash provided (used) by operating activities	129,248		268,642		272,962
FINANCING ACTIVITIES:
Cash distributions to parent	(154,800)		(137,900)		(166,500)
Net cash provided (used) by financing activities	(154,800)		(137,900)		(166,500)
INVESTING ACTIVITIES:
Property, plant and equipment:
Capital expenditures (1)	(124,932)		(106,729)		(78,787)
Contributions and advances for construction costs	6,066		10,555		10,268
Disposal of property, plant and equipment, net	(8,447)		(5,369)		(4,370)
Advances to affiliate, net	152,865		(29,199)		(33,573)
Net cash provided (used) in investing activities	25,552		(130,742)		(106,462)
Increase (decrease) in cash	—		—		—
Cash at beginning of period	—		—		—
Cash at end of period	$	—	$	—	$	—
____________________________________
(1) Increases to property, plant and equipment, exclusive of equity AFUDC	$	(139,620)	$	(109,359)	$	(88,791)
Changes in related accounts payable and accrued liabilities	14,688		2,630		10,004
Capital expenditures	$	(124,932)	$	(106,729)	$	(78,787)

See accompanying notes.

31

Northwest Pipeline LLC

Notes to Financial Statements

Note 1 – Summary of Significant Accounting Policies

Corporate Structure and Control

In this report, Northwest Pipeline LLC (Northwest) is at times referred to in the first person as “we,” “us” or “our.”

Northwest is indirectly owned by The Williams Companies, Inc. (Williams), a publicly traded Delaware corporation. Northwest is a single member limited liability company, and as such, single member losses are limited to the amount of its investment.

Nature of Operations

We own and operate an interstate pipeline system for the mainline transmission of natural gas. This system extends from the San Juan Basin in northwestern New Mexico and southwestern Colorado through Colorado, Utah, Wyoming, Idaho, Oregon and Washington to a point on the Canadian border near Sumas, Washington.

Summary of Significant Accounting Policies

Use of Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates.

Significant estimates and assumptions include:

•Litigation-related contingencies;

•Environmental remediation obligations;

•Impairment assessments of long-lived assets;

•Depreciation;

•Asset retirement obligations; and

•Measurement of regulatory assets and liabilities.

These estimates are discussed further throughout these notes.

Regulatory Accounting

We are regulated by the Federal Energy Regulatory Commission (FERC). Accounting Standards Codification (ASC) Topic 980, “Regulated Operations,” (Topic 980), provides that certain costs that would otherwise be charged to expense should be deferred as regulatory assets, based on the expected recovery from customers in future rates. Likewise, certain actual or anticipated credits that would otherwise reduce expense should be deferred as regulatory liabilities, based on the expected return to customers in future rates. Management's expected recovery of deferred costs and return of deferred credits generally results from specific decisions by regulators granting such ratemaking treatment. We record certain incurred costs and obligations as regulatory assets or liabilities if, based on regulatory orders or other available evidence, it is probable that the costs or obligations will be included in amounts allowable for recovery or refunded in future rates. Accounting for businesses that are regulated and apply the provisions of Topic 980 can differ from the accounting requirements for non-regulated businesses. Transactions that are recorded differently as a result of regulatory accounting requirements include the capitalization of an equity return component on regulated capital projects, capitalization of other project costs, retirements of general plant assets, levelized cost of service, negative salvage, asset retirement obligations (ARO), employee-related benefits, environmental costs, and other costs and taxes included in, or expected to be included in, future rates. As a rate-regulated entity, our management has determined that it is appropriate to apply the accounting prescribed by Topic 980, and, accordingly, the

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Northwest Pipeline LLC

Notes to Financial Statements

accompanying financial statements include the effects of the types of transactions described above that result from regulatory accounting requirements.

Revenue Recognition

Our customers are comprised of public utilities, municipalities, direct industrial users, electric power generators, and natural gas marketers and producers.

Service revenue contracts from our gas pipeline business contain a series of distinct services, with the majority of our contracts having a single performance obligation that is satisfied over time as the customer simultaneously receives and consumes the benefits provided by our performance.

Certain customers reimburse us for costs we incur associated with construction of property, plant, and equipment utilized in our operations. As a rate-regulated entity applying Topic 980, we follow FERC guidelines with respect to reimbursement of construction costs. FERC tariffs only allow for cost reimbursement and are non-negotiable in nature; thus, in our judgment, the construction activities do not represent an ongoing major and central operation of our gas pipeline business and are not within the scope of ASC Topic 606, “Revenues from Contracts with Customers.” Accordingly, cost reimbursements are treated as a reduction to the cost of the constructed asset.

Operating Revenues

We are subject to regulation by certain state and federal authorities, including the FERC, with revenue derived from both firm and interruptible transportation and storage contracts. Firm transportation and storage agreements provide for a fixed reservation charge based on the pipeline or storage capacity reserved, and a commodity charge based on the volume of natural gas delivered/stored, each at rates specified in our FERC tariffs or as negotiated with our customers, with contract terms that are generally long-term in nature. Most of our long-term contracts contain an evergreen provision, which allows the contracts to be extended for periods primarily up to one year in length an indefinite number of times following the specified contract term and until terminated generally by either us or the customer, but in certain cases unilaterally by the customer, with advance notice of termination ranging from one to five years. Interruptible transportation and storage agreements provide for a volumetric charge based on actual commodity transportation or storage utilized in the period in which those services are provided, and the contracts are generally limited to one-month periods or less. Our performance obligations include the following:

•Firm transportation or storage under firm transportation and storage contracts—an integrated package of services typically constituting a single performance obligation, which includes standing ready to provide such services and receiving, transporting or storing (as applicable), and redelivering commodities;

•Interruptible transportation and storage under interruptible transportation and storage contracts—an integrated package of services typically constituting a single performance obligation once scheduled, which includes receiving, transporting or storing (as applicable), and redelivering commodities.

In situations where, in our judgment, we consider the integrated package of services as a single performance obligation, which represents a majority of our contracts with customers, we do not consider there to be multiple performance obligations because the nature of the overall promise in the contract is to stand ready (with regard to firm transportation and storage contracts), receive, transport or store, and redeliver natural gas to the customer; therefore, revenue is recognized over time upon satisfaction of our daily stand ready performance obligation.

We recognize revenues for reservation charges over the performance obligation period, which is the contract term, regardless of the volume of natural gas that is transported or stored. Revenues for commodity charges from both firm and interruptible transportation services and storage services are recognized when natural gas is delivered at the agreed upon point or when natural gas is injected or withdrawn from the storage facility because they specifically relate to our efforts to provide these distinct services. Generally, reservation charges and commodity charges are recognized as revenue in the same period they are invoiced to our customers. As a result of the ratemaking process, certain amounts collected by us may be subject to refunds upon the issuance of final orders by the FERC in pending rate proceedings. We use judgment to record estimates of rate refund liabilities considering our and other third-party regulatory proceedings, advice of counsel, and other risks. At December 31, 2023 and 2022, we had no such rate refund liabilities.

In the course of providing transportation services to customers, we may receive different quantities of natural gas from customers than the quantities delivered on behalf of those customers or consumed in fuel to operate our system. The resulting

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Northwest Pipeline LLC

Notes to Financial Statements

customer imbalances are typically settled through the receipt or delivery of gas in the future based on the timelines outlined in Northwest’s tariff, whereas the over/under recovery of fuel is cleared up through Northwest’s semi-annual fuel tracker. Customer imbalances to be repaid or recovered in-kind are recorded as Exchange gas receivables or Exchange gas payables in our Balance Sheet. The under recovery of fuel is recorded as a Regulatory Asset and the over recovery is recorded as a Regulatory Liability. These imbalances are valued at published spot rates.

Contract Assets

Our contract assets consist of discounts provided to customers in the beginning of the contract term that are recognized on a straight-line basis over the entire contract term resulting in revenue recognition occurring prior to actual billings. Contract assets are included within Other on our Balance Sheet.

Contract Liabilities

Our contract liabilities consist of a fixed rate facility charge billed to customers that declines annually as specified per the tariff. These liabilities are classified as current or non-current according to when such amounts are expected to be recognized. Current and non-current liabilities are included within Accrued Liabilities and Other Long-Term Liabilities, respectively, on our Balance Sheet.

Leases

We are a lessee through noncancellable lease agreements for property and equipment consisting primarily of buildings, land, vehicles, and equipment used in both our operations and administrative functions. We recognize a lease liability with an offsetting right-of-use asset in our Balance Sheet for operating leases based on the present value of the future lease payments. We have elected to combine lease and nonlease components for all classes of leased assets in our calculation of the lease liability and the offsetting right-of-use asset.

Our lease agreements require both fixed and variable periodic payments, with initial terms typically ranging from one year to 30 years. Payment provisions in certain of our lease agreements contain escalation factors which may be based on stated rates or a change in a published index at a future time. The amount by which a lease escalates based on the change in a published index, which is not known at lease commencement, is considered a variable payment and is not included in the present value of the future lease payments, which only includes those that are stated or can be calculated based on the lease agreement at lease commencement. In addition to the noncancellable periods, many of our lease agreements provide for one or more extensions of the lease agreement for periods ranging from one year in length to an indefinite number of times following the specified contract term. Other lease agreements provide for extension terms that allow us to utilize the identified leased asset for an indefinite period of time so long as the asset continues to be utilized in our operations. In consideration of these renewal features, we assess the term of the lease agreements, which includes using judgment in the determination of which renewal periods and termination provisions, when at our sole election, will be reasonably certain of being exercised. Periods after the initial term or extension terms that allow for either party to the lease to cancel the lease are not considered in the assessment of the lease term. Additionally, we have elected to exclude leases with an original term of one year or less, including renewal periods, from the calculation of the lease liability and the offsetting right-of-use asset.

We use judgment in determining the discount rate upon which the present value of the future lease payments is determined. This rate is based on a collateralized interest rate corresponding to the term of the lease agreement using company, industry, and market information available.

Environmental Matters

We are subject to federal, state, and local environmental laws and regulations. Environmental expenditures are expensed or capitalized depending on their economic benefit and potential for rate recovery. We believe that expenditures required to meet applicable environmental laws and regulations are prudently incurred in the ordinary course of business and such expenditures would be permitted to be recovered through rates.

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Northwest Pipeline LLC

Notes to Financial Statements

Greenhouse Gas Emission Allowances

In accordance with the Climate Commitment Act of the state of Washington, which established a market-based cap-and-invest program, we are required to obtain emission allowances for the carbon emissions from nine of our thirteen compressor stations within the state of Washington whose annual carbon emissions exceed 25,000 metric tons of carbon dioxide equivalent. We record the purchased emission allowances at cost and the associated accumulated interest to a regulatory asset. The difference between the allowances held and the allowances required based on actual emissions for the period are measured using an estimate based on our most recent cost of allowances and accrued to a current liability and to a regulatory asset. Our Settlement allows us to recover the costs of purchasing allowances under the program in our next rate case.

Property, Plant, and Equipment

Property, plant and equipment, consisting principally of natural gas transmission facilities, is recorded at cost. The FERC identifies installation, construction and replacement costs that are to be capitalized and included in our asset base for recovery in rates. Routine maintenance, repairs, and renewal costs are charged to income as incurred. Gains or losses from the ordinary sale or retirement of property, plant and equipment are charged or credited to accumulated depreciation; certain other gains or losses are recorded in operating income.

We provide for depreciation under the composite (group) method at straight-line FERC prescribed rates that are applied to the cost of the group for transmission and storage facilities. Under this method, assets with similar lives and characteristics are grouped and depreciated as one asset. Included in our depreciation rates is a negative salvage component (net cost of removal) that we currently collect in rates. Our depreciation rates are subject to change each time we file a general rate case with the FERC.

The following table presents Total property, plant and equipment, net as presented on the Balance Sheet:

	Depreciation Rate	December 31,
		2023		2022
		(Thousands)
Transmission facilities	2.70%  -  10.20%	$	3,569,545	$	3,490,141
Storage facilities	1.60%  -  2.76%	155,433		142,326
Construction in progress	Not applicable	84,945		44,702
Other	0% - 33.33%	164,977		159,085
Property, plant and equipment		3,974,900		3,836,254
Less-Accumulated depreciation and amortization		2,026,007		1,941,806
Total property, plant and equipment, net		$	1,948,893	$	1,894,448

We record a liability and increase the basis in the underlying asset for the present value of each expected future ARO at the time the liability is initially incurred, typically when the asset is acquired or constructed. Measurement of ARO includes, as a component of future expected costs, an estimate of the price that a third party would demand, and could expect to receive, for bearing the uncertainties inherent in the obligations, sometimes referred to as market-risk premium. We measure changes in the liability due to passage of time by applying an interest method of allocation. This amount is recognized as an increase in the carrying amount of the liability and is offset by a regulatory asset. The gross regulatory asset balances associated with ARO as of December 31, 2023 and 2022 were $116.2 million and $109.0 million, respectively. The regulatory asset is expected to be fully recovered through the negative salvage component of depreciation included in our rates; as such, that amount of the negative salvage component of accumulated depreciation has been reclassified and netted against the amount of the ARO regulatory asset to result in a regulatory liability of $30.7 million and $30.6 million at December 31, 2023 and 2022, respectively.

Allowance for Funds Used During Construction

Allowance for funds used during construction (AFUDC) represents the estimated cost of borrowed and equity funds applicable to utility plant in process of construction and is included as a cost of property, plant and equipment because it

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Northwest Pipeline LLC

Notes to Financial Statements

constitutes an actual cost of construction under established regulatory practices. The FERC has prescribed a formula to be used in computing separate allowances for borrowed and equity AFUDC. The allowance for borrowed funds used during construction was $0.7 million for 2023, $0.7 million for 2022, and $0.2 million for 2021. The allowance for equity funds was $3.1 million, $2.3 million, and $1.4 million for 2023, 2022, and 2021, respectively.

Income Taxes

We are a natural gas company organized as a pass-through entity and our taxable income or loss is consolidated on the federal income tax return of our parent, Williams. We generally are treated as a pass-through entity for state and local income tax purposes, and those taxes are generally borne on a consolidated basis by Williams. Net income for financial statement purposes may differ significantly from taxable income of Williams as a result of differences between the tax basis and financial reporting basis of assets and liabilities.

Accounts Receivable

Accounts receivable are carried on a gross basis less an allowance for doubtful accounts. We estimate the allowance for doubtful accounts, considering current expected credit losses using a forward-looking “expected loss” model, the financial condition of our customers, and the age of past due accounts. The majority of our trade receivable balances are due within 30 days. We monitor the credit quality of our counterparties through review of collection trends, credit ratings, and other analyses, such as bankruptcy monitoring, if applicable. Financial assets are evaluated as one pool. Changes in counterparty risk factors could lead to reassessment of the composition of our financial assets as one pool. We calculate our allowance for credit losses incorporating an aging method. In estimating our expected credit losses, we utilized historical loss rates over many years. Our expected credit loss estimate considered both internal and external forward-looking commodity price expectations, as well as counterparty credit ratings, and factors impacting their near-term liquidity.

We do not offer extended payment terms and typically receive payment within one month. We consider receivables past due if full payment is not received by the contractual due date. Past due accounts are generally written off against the allowance for doubtful accounts only after all collection attempts have been exhausted. We do not have a material amount of significantly aged receivables at December 31, 2023 and 2022.

Materials and Supplies Inventory

All materials and supplies inventory is stated at average cost. We perform an annual review of materials and supplies inventories, including a quarterly analysis of parts that may no longer be useful due to planned replacements of compressor engines and other components on our system. Based on this assessment, we record a reserve for the value of the inventory which can no longer be used for maintenance and repairs on our pipeline. The reserve for inventory was $1.0 million at December 31, 2023, and there was a minimal reserve at December 31, 2022.

Contingent Liabilities

We record liabilities for estimated loss contingencies, including environmental matters, when we assess that a loss is probable and the amount of the loss can be reasonably estimated. These liabilities are calculated based upon our assumptions and estimates with respect to the likelihood or amount of loss and upon advice of legal counsel, engineers, or other third-parties regarding the probable outcomes of the matters. These calculations are made without consideration of any potential recovery from third-parties. We recognize insurance recoveries or reimbursements from others when realizable. Revisions to these liabilities are generally reflected in income when new or different facts or information become known or circumstances change that affect the previous assumptions or estimates.

Pension and Other Postretirement Benefits

We do not have employees. Certain of the costs charged to us by Williams associated with employees who directly support us include costs related to Williams’ pension and other postretirement benefit plans (see Note 7 – Benefit Plans). Although the underlying benefit plans of Williams are single-employer plans, we follow multiemployer plan accounting whereby the amount charged to us, and thus paid by us, is based on our share of net periodic benefit cost.

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Northwest Pipeline LLC

Notes to Financial Statements

Cash Flows from Operating Activities

We use the indirect method to report cash flows from operating activities, which requires adjustments to net income to reconcile to net cash flows provided by operating activities.

Interest Payments

Cash payments for interest, net of interest capitalized, were $26.1 million in 2023, 2022 and 2021.

Note 2 – Revenue Recognition

Revenue by Category

Our revenue disaggregation by major service line includes Natural gas transportation, Natural gas storage, and Other, which are separately presented on the Statement of Net Income.

Contract Assets

The following table presents a reconciliation of our contract assets:

	Year Ended December 31,
	2023		2022
	(Thousands)
Balance at beginning of period	$	12,490	$	7,943
Revenue recognized in excess of amounts invoiced	4,316		4,547
Balance at end of period	$	16,806	$	12,490

Contract Liabilities

The following table presents a reconciliation of our contract liabilities:

	Year Ended December 31,
	2023		2022
	(Thousands)
Balance at beginning of period	$	2,643	$	3,672
Recognized in revenue	(1,175)		(1,029)
Balance at end of period	$	1,468	$	2,643

Remaining Performance Obligations

Our remaining performance obligations primarily include reservation charges on contracted capacity on our firm transportation and storage contracts with customers. Amounts from certain contracts included in the table below, which are subject to periodic review and approval by the FERC, reflect the rates for such services in our current FERC tariffs for the life of the related contracts; however, these rates may change based on future rate cases or settlements approved by the FERC. This table excludes the variable consideration component for commodity charges. Certain of our contracts contain evergreen and other renewal provisions for periods beyond the initial term of the contract. The remaining performance obligations as of December 31, 2023, do not consider potential future performance obligations for which the renewal has not been exercised and exclude contracts with customers for which the underlying facilities have not received FERC authorization to be placed into service.

The following table presents the amount of the contract liabilities balance expected to be recognized as revenue when performance obligations are satisfied and the transaction price allocated to the remaining performance obligations under certain contracts as of December 31, 2023.

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Northwest Pipeline LLC

Notes to Financial Statements

	Contract Liabilities		Remaining Performance Obligations
	(Thousands)
2024 (one year)	$	1,178	$	386,252
2025 (one year)	290		369,844
2026 (one year)	—		354,605
2027 (one year)	—		351,285
2028 (one year)	—		345,753
Thereafter	—		2,228,679
Total	$	1,468	$	4,036,418

Accounts Receivable

Receivables from contracts with customers are included within Receivables - Trade and Receivables - Affiliates and receivables that are not related to contracts with customers are included within the balance of Receivables - Advances to affiliate and Receivables - Other in our Balance Sheet.

Note 3 – Leases

We are a lessee through non-cancellable lease agreements for property and equipment consisting primarily of buildings, land, vehicles, and equipment used in both our operations and administrative functions.

	Year Ended December 31,
	2023		2022		2021
	(Thousands)
Lease Cost:
Operating lease cost	$	1,205	$	1,226		$	1,334
Variable lease cost	588		578			681
Total lease cost	$	1,793	$	1,804		$	2,015
Cash paid for operating lease liabilities	$	954	$	950		$	2,395
			December 31,
			2023			2022
			(Thousands)
Other Information:
Right-of-use assets			$	8,725		$	9,621
Operating lease liabilities:
Current (included in Accrued liabilities - Other on our Balance Sheet)			$	701		$	681
Lease liability			$	7,193		$	7,857
Weighted-average remaining lease term - operating leases (years)			15			16
Weighted-average discount rate - operating leases			4.18%			4.12%

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Northwest Pipeline LLC

Notes to Financial Statements

As of December 31, 2023, the following table represents our operating lease maturities, including renewal provisions that we have assessed as being reasonably certain of exercise, for each of the years ended December 31:

	(Thousands)
2024	$	954
2025	971
2026	973
2027	987
2028	961
Thereafter	6,651
Total future lease payments	11,497
Less amount representing interest	3,603
Total obligations under operating leases	$	7,894

Note 4 – Rate and Regulatory Matters

Rate Case Settlement

On November 15, 2022, the FERC approved our Petition for Approval of Pre-Filing Stipulation and Settlement Agreement (Settlement) in Docket No. RP22-1155. The Settlement establishes a new general system firm Rate Schedule TF-1 (Large Customer) daily reservation rate of $0.37250/Dth with a $0.00935/Dth commodity rate (which were made effective January 1, 2023), resolved other rate issues, established a Modernization and Emission Reduction Program and satisfies our rate case filing obligation under our settlement in Docket No. RP17-346. Provisions were included in the Settlement that establish a moratorium on any Natural Gas Act of 1938, as amended (NGA) Section 4 or 5 proceedings that would seek to place new rates in effect any earlier than January 1, 2026. The Settlement also provides that we file an NGA Section 4 general rate case with rates to be effective not later than April 1, 2028, unless (a) we have entered into a pre-filing settlement or (b) a Section 5 general rate case has been filed on or before April 1, 2028.

As a result of the Settlement, in January 2023, we refunded approximately $126 million, including interest, associated with the decrease in federal tax rates due to Tax Reform, which reduced Accrued liabilities - Regulatory liabilities on our Balance Sheet.

Note 5 – Contingent Liabilities and Commitments

Environmental Matters

Beginning in the mid-1980s, we evaluated many of our facilities for the presence of toxic and hazardous substances to determine to what extent, if any, remediation might be necessary. We identified polychlorinated biphenyl (PCB) contamination in air compressor systems, soils, and related properties at certain compressor station sites. Similarly, we identified hydrocarbon impacts at these facilities due to the former use of earthen pits, lubricating oil leaks or spills, and excess pipe coating released to the environment. In addition, heavy metals have been identified at these sites due to the former use of mercury containing meters and paint and welding rods containing lead, cadmium, and arsenic. The PCBs were remediated pursuant to a Consent Decree with the U.S. Environmental Protection Agency (EPA) in the late 1980s, and we conducted a voluntary clean-up of the hydrocarbon and mercury impacts in the early 1990s. In 2005, the Washington Department of Ecology required us to re-evaluate our previous clean-ups in Washington. During 2006 to 2015, 129 meter stations were evaluated, of which 82 required remediation. As of December 31, 2023, two meter stations are still being remediated. During 2006 to 2018, 14 compressor stations were evaluated, of which 11 required remediation. As of December 31, 2023, four compressor stations are still being remediated. At December 31, 2023, we had accrued liabilities totaling approximately $1.0 million, $0.2 million of which is recorded in Accrued liabilities - Other and $0.8 million of which is recorded in Other Long-Term Liabilities - Other on the Balance Sheet. At December 31, 2022, we had accrued liabilities totaling approximately $1.0 million, $0.1 million of which is recorded in Accrued liabilities - Other and $0.9 million of which is recorded in Other Long-Term Liabilities - Other on the Balance Sheet. We are conducting environmental assessments and implementing a variety of remedial measures that may result in increases or decreases in the total estimated costs.

The EPA and various state regulatory agencies routinely propose and promulgate new rules, and issue updated guidance to existing rules. These rulemakings include, but are not limited to, rules for reciprocating internal combustion engine and

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Northwest Pipeline LLC

Notes to Financial Statements

combustion turbine maximum achievable control technology, review and updates to the National Ambient Air Quality Standards, and rules for new and existing source performance standards for volatile organic compounds and methane. We continuously monitor these regulatory changes and how they may impact our operations. Implementation of new or modified regulations may result in impacts to our operations and increase the cost of additions to Total property, plant, and equipment, net on the Balance Sheet for both new and existing facilities in affected areas; however, due to regulatory uncertainty on final rule content and applicability timeframes, we are unable to reasonably estimate the cost of these regulatory impacts at this time.

Environmental expenditures are expensed or capitalized depending on their future economic benefit and potential for rate recovery. We believe that, with respect to any expenditures required to meet applicable standards and regulations, the FERC would grant the requisite rate relief so that substantially all of such expenditures would be permitted to be recovered through rates.

Washington State Climate Commitment Act

In 2021, the state of Washington passed its Climate Commitment Act establishing a market-based cap-and-invest program to reduce carbon emissions. This program took effect on January 1, 2023, and sets a limit, or cap, on overall carbon emissions in the state and requires businesses like ours to obtain allowances equal to their annual covered carbon emissions. The state’s cap will be reduced over time to meet the state’s carbon emissions reduction targets, which means fewer carbon emissions allowances will be available to purchase each year. These allowances can be purchased through quarterly auctions hosted by the state or bought and sold on a secondary market. In 2023, we began purchasing allowances for the carbon emissions from nine of our thirteen compressor stations within the state whose annual carbon emissions exceed 25,000 metric tons of carbon dioxide equivalent. We also began purchasing allowances for our delivery of natural gas to certain of our customers and certain of our facilities in the state whose annual carbon emissions are insufficient to require their direct participation in the program. Our Settlement allows us to recover the costs of purchasing allowances under the program in our next rate case.

As of December 31, 2023 a total of $22.3 million was included in Other Assets - Regulatory assets on our Balance Sheet and was comprised of the cost of the purchased allowances held, the estimated difference between the allowances held and the allowances required, and the interest income component of the regulatory asset. At December 31, 2023, $3.7 million was included in Accrued liabilities - Other on our Balance Sheet as the estimated difference. The interest income is reflected in Miscellaneous other (income) expense, net on our Statement of Net Income and was $0.6 million for the year ended December 31, 2023.

Other Matters

Various other proceedings are pending against us and are considered incidental to our operations.

Summary

We have disclosed all significant matters for which we are unable to reasonably estimate a range of possible loss. We estimate that for all matters for which we are able to reasonably estimate a range of loss, including those noted above and others that are not individually significant, our aggregate reasonably possible losses beyond amounts accrued for all of our contingent liabilities are immaterial to our expected future annual results of operations, liquidity and financial position. These calculations have been made without consideration of any potential recovery from third-parties. 

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Northwest Pipeline LLC

Notes to Financial Statements

Note 6 – Debt and Financing Arrangements

Long-Term Debt 

	December 31,
	2023		2022
	(Thousands)
7.125% Debentures due 2025	$	85,000	$	85,000
4.0% Notes due 2027	500,000		500,000
Unamortized debt issuance costs	(1,954)		(2,517)
Unamortized debt discount	(1,868)		(2,400)
Total long-term debt	$	581,178	$	580,083

The following table reflects future maturities of long-term (at face value) debt for the next five years (in thousands):

2025	$	85,000
2027	$	500,000

No property is pledged as collateral under any of our long-term debt.

Credit Facility

In October 2021, we along with Williams and Transcontinental Gas Pipe Line Company, LLC (Transco), the lenders named therein, and an administrative agent entered into an amended and restated credit agreement (Credit Agreement) that reduced aggregate commitments available from $4.5 billion to $3.75 billion, with up to an additional $500 million increase in aggregate commitments available under certain circumstances. The Credit Agreement was effective on October 8, 2021. In the second quarter of 2023, the maturity date of our Credit Agreement was extended one year and now expires October 8, 2027. The amended Credit Agreement allows the co-borrowers to request up to two extensions of the maturity date each for an additional one-year period to allow a maturity date as late as October 8, 2029, under certain circumstances. Additionally, the amended Credit Agreement replaces the London Interbank Offered Rate with the Term Secured Overnight Financing Rate as the benchmark interest rate index. The Credit Agreement allows for swing line loans up to an aggregate of $200 million, subject to available capacity under the credit facility, and letters of credit commitments of $500 million. We and Transco are each able to borrow up to $500 million under this credit facility to the extent not otherwise utilized by the other co-borrowers. At December 31, 2023, no letters of credit have been issued and no loans to Williams were outstanding under the credit facility.

The Credit Agreement contains the following terms and conditions:

•Various covenants may limit, among other things, a borrower’s and its material subsidiaries’ ability to grant certain liens supporting indebtedness, merge or consolidate, sell all or substantially all of its assets in certain circumstances, make certain distributions during an event of default, and each borrower and each borrower’s respective material subsidiaries’ ability to enter into certain restrictive agreements.

•If an event of default with respect to a borrower occurs under the credit facility, the lenders will be able to terminate the commitments for the respective borrowers and accelerate the maturity of the loans of the defaulting borrower under the credit facility and exercise other rights and remedies.

•Other than swing line loans, each time funds are borrowed, the applicable borrower may choose from two methods of calculating interest: a fluctuating base rate equal to an alternative base rate as defined in the Credit Agreement plus an applicable margin or a periodic fixed rate equal to the Term Secured Overnight Financing Rate plus an applicable margin. Williams is required to pay a commitment fee based on the unused portion of the credit facility. The applicable margin is determined by reference to a pricing schedule based on the applicable borrower’s senior unsecured long-term debt ratings and the commitment fee is determined by reference to a pricing schedule based on Williams’ senior unsecured long-term debt ratings.

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Northwest Pipeline LLC

Notes to Financial Statements

The ratio of debt to capitalization (defined as net worth plus debt), each as defined in the Credit Agreement, must be no greater than 65 percent for each of Transco and Northwest.

Commercial Paper Program

Williams has a $3.5 billion commercial paper program. Williams’ management considers amounts outstanding under this program to be a reduction of available capacity under the credit facility. At December 31, 2023, Williams had $725 million of commercial paper outstanding, which was paid down in January 2024.

Restrictive Debt Covenants

At December 31, 2023, none of our debt instruments restrict the amount of distributions to our parent, provided, however, that under the credit facility described above, we are restricted from making distributions to our parent during an event of default if we have directly incurred indebtedness under the credit facility. Our debt agreements contain restrictions on our ability to incur secured debt beyond certain levels. At December 31, 2023, we were in compliance with the covenants contained in our credit agreements and indentures.

Note 7 – Benefit Plans

Certain of the benefit costs charged to us by Williams associated with employees who directly support us are described below. Additionally, allocated corporate expenses from Williams to us also include amounts related to these same employee benefits, which are not included in the amounts presented below (see Note 9 – Transactions With Major Customers and Affiliates).

Pension and Other Postretirement Benefit Plans

Williams has noncontributory defined benefit pension plans (Williams Pension Plan, Williams Inactive Employees Pension Plan, and The Williams Companies Retirement Restoration Plan) that provide pension benefits for its eligible employees hired prior to January 1, 2019. We received pension credits from Williams of $0.2 million in 2023, and pension charges of $0.7 million in 2022 and $0.8 million in 2021.

Williams provides subsidized retiree medical benefits to a closed group of participants as well as retiree life insurance to eligible participants. During 2023, 2022, and 2021, we received credits from Williams related to retiree medical and life insurance benefits of $0.2 million, $1.2 million and $1.6 million, respectively. These credits were recorded as regulatory liabilities.

We have been allowed by rate case settlements to collect or refund in future rates any differences between the actuarially determined costs and amounts currently being recovered in rates related to other postretirement benefits. Any differences between the annual actuarially determined cost and amounts currently being recovered in rates are recorded as regulatory assets or liabilities and collected or refunded through future rate adjustments. The amounts of other postretirement benefits costs deferred as regulatory liabilities at December 31, 2023 and 2022 are $42.4 million and $42.2 million, respectively.

Defined Contribution Plan

Williams maintains a defined contribution plan for substantially all of its employees. Williams charged us compensation expense of $3.0 million in 2023, $2.8 million in 2022 and $2.7 million in 2021 for Williams’ company contributions to this plan.

Employee Stock-Based Compensation Plan Information

The Williams Companies, Inc. 2007 Incentive Plan (the Plan), as subsequently amended and restated, provides for Williams’ common stock-based awards to both employees and non-management directors. The Plan permits the granting of various types of awards including, but not limited to, restricted stock units and stock options. Awards may be granted for no consideration other than prior and future services or based on certain financial performance targets achieved.

42

Northwest Pipeline LLC

Notes to Financial Statements

Williams currently bills us directly for compensation expense related to stock-based compensation awards based on the fair value of the awards. We are also billed for our proportionate share of Williams’ and other affiliates’ stock-based compensation expense through various allocation processes.

Total stock-based compensation expense for the years ended December 31, 2023, 2022 and 2021 was $1.5 million, $1.3 million and $1.2 million, respectively, excluding amounts allocated from Williams.

Note 8 – Fair Value Measurements

Fair Value Methods

The following methods and assumptions were used to estimate the fair value of each class of financial instruments for which it is practicable to estimate that value:

Short-term financial assets: The carrying values of short-term financial assets that have variable interest rates (advances to affiliate), accounts receivable and accounts payable approximate fair value because of the short-term nature of these instruments.

Long-term debt: The disclosed fair value of our long-term debt, which we consider as a level 2 measurement, is determined by a market approach using broker quoted indicative period-end bond prices. The quoted prices are based on observable transactions in less active markets for our debt or similar instruments. The carrying amount and estimated fair value of our long-term debt, including current maturities, were $581.2 million and $581.1 million, respectively, at December 31, 2023, and $580.1 million and $560.2 million, respectively, at December 31, 2022.

Note 9 – Transactions with Major Customers and Affiliates

Major Customers

During the periods presented, more than 10 percent of our operating revenues were generated from each of the following customers:

	Year Ended December 31,
	2023		2022		2021
	(Thousands)
Puget Sound Energy, Inc.	$	126,206	$	130,705	$	131,462
Cascade Natural Gas Corporation	47,046		48,664		49,078
Northwest Natural Gas Company	46,637		48,921		48,901

Our major customers are located in the Pacific Northwest. As a general policy, collateral is not required for receivables, but customers’ financial condition and credit worthiness are regularly evaluated and historical collection losses have been minimal.

Affiliates

We are a participant in Williams’ cash management program. At December 31, 2023 and 2022, our advances to Williams totaled approximately $157.8 million and $310.6 million, respectively. These advances are represented by demand notes and are classified as Receivables - Advances to affiliate on the Balance Sheet. The interest rate on these intercompany demand notes is based upon the daily overnight investment rate paid on Williams’ excess cash at the end of each month, which was approximately 5.2 percent at December 31, 2023. The interest income from these advances was $8.3 million and $4.9 million for the years ended December 31, 2023 and 2022, respectively. The interest income from these advances was minimal for the year ended December 31, 2021. Such interest income is included in Other (Income) and Other Expenses - Miscellaneous other (income) expense, net on the Statement of Net Income.

We have no employees. Services necessary to operate our business are provided to us by Williams and certain affiliates of Williams. We reimburse Williams and its affiliates for all direct and indirect expenses incurred or payments made (including salary, bonus, incentive compensation, and benefits) in connection with these services. Employees of Williams also provide general, administrative and management services to us, and we are charged for certain administrative expenses incurred by

43

Northwest Pipeline LLC

Notes to Financial Statements

Williams. These charges are either directly identifiable or allocated to our assets. Direct charges are for goods and services provided by Williams at our request. Allocated charges are based on a three-factor formula, which considers revenues; property, plant, and equipment; and payroll. In management’s estimation, the allocation methodologies used are reasonable and result in a reasonable allocation to us of our costs of doing business incurred by Williams. We have recorded $86.0 million, $87.7 million, and $85.2 million for the years ended December 31, 2023, 2022, and 2021, respectively, for these service expenses, which are primarily included in Operation and maintenance and General and administrative expenses on the Statement of Net Income.

During January 2024, we declared and paid a cash distribution of $33.0 million to our parent.

Note 10 – Asset Retirement Obligations

Our accrued asset retirement obligations relate to our gas storage and transmission facilities. At the end of the useful life of our facilities, we are legally obligated to remove or plug and abandon certain transmission facilities including underground pipelines, major river spans, compressor stations and meter station facilities. These obligations also include restoration of the property sites after removal of the facilities from above and below the ground. Our overall asset retirement obligation changed as follows:

	Year Ended December 31,
	2023		2022
	(Thousands)
Beginning balance	$	129,306	$	122,650
Accretion	7,017		6,656
Changes in estimates of existing obligations (1)	(60)		—
Ending balance	$	136,263	$	129,306

______________________

(1)    Changes in estimates of existing obligations are primarily due to the annual review process, which considers various factors including inflation rate, current estimates for removal costs, discount rates, and the estimated remaining life of assets.

44

Northwest Pipeline LLC

Notes to Financial Statements

Note 11 – Regulatory Assets and Liabilities

The regulatory assets and regulatory liabilities resulting from our application of the provisions of Topic 980 included on the accompanying Balance Sheet are as follows:

	December 31,
	2023		2022
	(Thousands)
Current regulatory assets:
Fuel recovery	$	19	$	11,871
Levelized depreciation	2,035		1,694
Total current regulatory assets	2,054		13,565
Long-term regulatory assets:
Levelized depreciation	9,519		11,601
Grossed-up deferred taxes on equity funds used during construction	3,969		4,350
Washington State Carbon and Greenhouse Gas Tax	22,308		—
Total long-term regulatory assets	35,796		15,951
Total regulatory assets	$	37,850	$	29,516
Current regulatory liabilities:
Customer tax refund	$	—	$	125,506
Deferred federal taxes - liability	18,643		18,643
Deferred state taxes - liability	1,094		1,094
Fuel recovery	1,637		—
Total current regulatory liabilities	21,374		145,243
Long-term regulatory liabilities:
Deferred federal taxes - liability	169,240		187,883
Postretirement benefits	42,415		42,207
Asset retirement obligations, net	30,685		30,590
Deferred state taxes - liability	9,932		11,026
Total long-term regulatory liabilities	252,272		271,706
Total regulatory liabilities	$	273,646	$	416,949

The significant regulatory assets and liabilities include:

Fuel Recovery: This amount represents the value of the cumulative volumetric difference between the gas retained from our customers and the gas consumed in operations. These amounts are not included in the rate base but assets and liabilities are expected to be recovered or refunded, respectively, by changing the fuel reimbursement rate in subsequent annual fuel filings.

Levelized Depreciation: Levelized depreciation allows contract revenue streams to remain constant over the primary contract terms by recognizing lower than book depreciation in the early years and higher than book depreciation in later years. The depreciation component of the levelized incremental rates will equal the accumulated book depreciation by the end of the primary contract terms. The difference between levelized depreciation and straight-line book depreciation is recorded as a FERC approved regulatory asset or liability and is eliminated over the levelization period.

Grossed-Up Deferred Taxes on Equity Funds Used During Construction: The regulatory asset balance was established to offset the deferred tax for the equity component of the allowance for funds used during the construction of long-lived assets. All amounts were generated during the period that we were a taxable entity. Taxes on capitalized funds used during construction and the offsetting deferred income taxes are included in the rate base and are recovered over the depreciable lives of the long-lived assets to which they relate.

45

Northwest Pipeline LLC

Notes to Financial Statements

Customer Tax Refund: In our 2017 Settlement, which became effective January 1, 2018, we agreed with our customers that if federal income tax rates decreased due to subsequent legislation, such as the Tax Cuts and Jobs Act of 2017 (Tax Reform), we would record a regulatory liability. As a result of Tax Reform and as stipulated in the Docket No. RP22-1155 rate case settlement, the accrued regulatory liability, including interest, was paid to customers in January 2023.

Deferred Federal Taxes - Liability: This regulatory liability balance was established as a result of a decrease to rate base deferred taxes due to a decrease to the effective federal income tax rate. The timing of the refund of the regulatory liability to rate payers is stated in the Docket No. RP22-1155 rate case settlement.

Postretirement Benefits: We seek to recover the actuarially determined cost of postretirement benefits through rates that are set through periodic general rate filings. Any differences between the annual actuarially determined cost and amounts currently being recovered in rates are recorded as regulatory assets or liabilities and collected or refunded through future rate adjustments. These amounts are not included in the rate base, and we are not currently recovering postretirement benefit costs in our rates (see Note 7 – Benefit Plans).

ARO, net: This regulatory liability balance reflects the amount that we have recovered in our rates related to our future retirement costs offset by depreciation of the ARO asset and changes in the ARO liability due to the passage of time. AROs are expected to be fully recovered through the net negative salvage component of depreciation included in our rates (see Note 10 – Asset Retirement Obligations).

Deferred State Taxes - Liability: This regulatory liability balance, following the August 10, 2018 merger of Williams with Williams Partners L.P., reflects a decrease to rate base deferred taxes due to a decrease to the estimated effective state income tax rates. The timing of the refund of the regulatory liability to rate payers is stated in the Docket No. RP22-1155 rate case settlement.

Washington State Carbon and Greenhouse Tax: This amount represents the cost of emission allowances and the associated accumulated interest as a result of the passage of the state of Washington Climate Commitment Act that took effect January 1, 2023. Our Settlement allows us to recover the costs of purchasing allowances under the program in our next rate case.

46

Item 9. Changes in and Disagreements With Accountants on Accounting and Financial Disclosure

None.

Item 9A. Controls and Procedures

Disclosure Controls and Procedures

Our management, including our Senior Vice President and our Vice President and Chief Accounting Officer, does not expect that our disclosure controls and procedures (as defined in Rules 13a - 15(e) and 15d - 15(e) of the Securities Exchange Act, as amended) (Disclosure Controls) or our internal control over financial reporting (Internal Controls) will prevent all errors and all fraud. A control system, no matter how well conceived and operated, can provide only reasonable, not absolute, assurance that the objectives of the control system are met. Further, the design of a control system must reflect the fact that there are resource constraints, and the benefits of controls must be considered relative to their costs. Because of the inherent limitations in all control systems, no evaluation of controls can provide absolute assurance that all control issues and instances of fraud, if any, within the company have been detected. These inherent limitations include the realities that judgments in decision-making can be faulty, and that breakdowns can occur because of simple error or mistake. Additionally, controls can be circumvented by the individual acts of some persons, by collusion of two or more people, or by management override of the control. The design of any system of controls also is based in part upon certain assumptions about the likelihood of future events, and there can be no assurance that any design will succeed in achieving its stated goals under all potential future conditions. Because of the inherent limitations in a cost-effective control system, misstatements due to error or fraud may occur and not be detected. We monitor our Disclosure Controls and Internal Controls and make modifications as necessary; our intent in this regard is that the Disclosure Controls and Internal Controls will be modified as systems change and conditions warrant.

Evaluation of Disclosure Controls and Procedures

An evaluation of the effectiveness of the design and operation of our Disclosure Controls was performed as of the end of the period covered by this report. This evaluation was performed under the supervision and with the participation of our management, including our Senior Vice President and our Vice President and Chief Accounting Officer. Based upon that evaluation, our Senior Vice President and our Vice President and Chief Accounting Officer concluded that these Disclosure Controls are effective at a reasonable assurance level.

Changes in Internal Control over Financial Reporting

There have been no changes during the fourth quarter of 2023 that have materially affected, or are reasonably likely to materially affect, our Internal Control over Financial Reporting.

Management’s Annual Report on Internal Control over Financial Reporting

Management is responsible for establishing and maintaining adequate internal control over financial reporting (as defined in Rules 13a - 15(f) and 15d - 15(f) under the Securities Exchange Act of 1934). Our internal control over financial reporting is designed to provide reasonable assurance to our management regarding the preparation and fair presentation of financial statements in accordance with accounting principles generally accepted in the United States. Our internal control over financial reporting includes those policies and procedures that (i) pertain to the maintenance of records that, in reasonable detail, accurately and fairly reflect the transactions and dispositions of our assets; (ii) provide reasonable assurance that transactions are recorded as to permit preparation of financial statements in accordance with generally accepted accounting principles, and that our receipts and expenditures are being made only in accordance with authorization of our management; and (iii) provide reasonable assurance regarding prevention or timely detection of unauthorized acquisition, use or disposition of our assets that could have a material effect on our financial statements.

All internal control systems, no matter how well designed, have inherent limitations including the possibility of human error and the circumvention or overriding of controls. Therefore, even those systems determined to be effective can provide only reasonable assurance with respect to financial statement preparation and presentation.

Under the supervision and with the participation of our management, including our Senior Vice President and our Vice President and Chief Accounting Officer, we assessed the effectiveness of our internal control over financial reporting as of December 31, 2023, based on the criteria set forth by the Committee of Sponsoring Organizations of the Treadway Commission

47

(COSO) in Internal Control — Integrated Framework (2013). Based on our assessment, we concluded that, as of December 31, 2023, our internal control over financial reporting was effective.

This annual report does not include a report of our registered public accounting firm regarding internal control over financial reporting. A report by our registered public accounting firm is not required pursuant to rules of the Securities and Exchange Commission that permit us to provide only management’s report in this annual report.

Item 9B. Other Information

None.

Item 9C. Disclosure Regarding Foreign Jurisdictions that Prevent Inspections

None.

PART III

Since we meet the conditions set forth in General Instruction (I)(1)(a) and (b) of Form 10-K, the information required by Items 10, 11, 12, and 13 is omitted.

Item 14. Principal Accounting Fees and Services

Fees for professional services provided by our independent registered public accounting firm in each of the last two fiscal years in each of the following categories are (in millions):

	Year Ended December 31,
	2023		2022
Audit fees	$	0.6	$	0.6
Audit-related fees	—		—
Tax fees	—		—
All other fees	—		—
Total fees	$	0.6	$	0.6

Fees for audit services include fees associated with the annual audit, the reviews for our quarterly reports on Form 10-Q, the reviews for other SEC and FERC filings, and accounting consultation.

As a wholly owned subsidiary of Williams, we do not have a separate audit committee. The Williams Audit Committee is responsible for the appointment, compensation, retention, and oversight of Ernst & Young LLP (EY) as such appointment relates to us and Williams’ other affiliates. The Williams Audit Committee is responsible for overseeing the determination of fees associated with EY’s audit of our financial statements. The Williams Audit Committee has established a policy regarding pre-approval of all audit and non-audit services provided by EY to Williams and its affiliates. On an ongoing basis, management presents specific projects and categories of service, including projects and categories of service relating to us, to the Williams Audit Committee to request advance approval. The Williams Audit Committee reviews those requests and advises management if the Williams Audit Committee approves the engagement of EY. On a periodic basis, management reports to the Williams Audit Committee regarding the actual spending for such projects and services compared to the approved amounts. The Williams Audit Committee may also delegate the authority to pre-approve audit and permitted non-audit services, excluding services related to internal control over financial reporting, to a subcommittee of one or more committee members, provided that any such pre-approvals are reported on at a subsequent Williams Audit Committee meeting.

48

PART IV

Item 15. Exhibits and Financial Statement Schedules

	Page Reference to 2023 Form 10-K
(a) 1. and 2. Northwest Pipeline LLC financial statements and schedules
Index
Covered by reports of independent auditors:
Statement of Net Income for the Years Ended December 31, 2023, 2022, and 2021	27
Balance Sheet at December 31, 2023 and 2022	28
Statement of Changes in Member’s Equity for the Years Ended December 31, 2023, 2022, and 2021	30
Statement of Cash Flows for the Years Ended December 31, 2023, 2022, and 2021	31
Notes to Financial Statements	32

All other schedules have been omitted since the required information is not present or is not present in amounts sufficient to require submission of the schedule, or because the information required is included in the financial statements and notes thereto.

49

(a) 3 and b. Exhibits:

Exhibit	Description
2	Certificate of Conversion of Northwest Pipeline GP (filed on July 3, 2013 as Exhibit 2.1 to our current report on Form 8-K (File No. 001-07414) and incorporated herein by reference).
3.1	Certificate of Formation of Northwest Pipeline LLC (filed on July 3, 2013 as Exhibit 2.2 to our current report on Form 8-K (File No. 001-07414) and incorporated herein by reference).
3.2	Operating Agreement of Northwest Pipeline LLC (filed on July 3, 2013 as Exhibit 3.1 to our current report on Form 8-K (File No. 001-07414) and incorporated herein by reference).
4.1	Senior Indenture, dated as of November 30, 1995 between Northwest Pipeline Corporation and Chemical Bank, relating to Northwest Pipeline’s 7.125% Debentures due 2025 (filed on September 14, 1995 as Exhibit 4.1 to our registration statement on Form S-3 (File No. 033-62639) and incorporated herein by reference).
4.2	Indenture, dated as of April 3, 2017, between Northwest Pipeline LLC and The Bank of New York Mellon Trust Company, N.A., as trustee (filed on April 3, 2017 as Exhibit 4.1 to our current report on Form 8-K (File No. 001-07414) and incorporated herein by reference).
10.1	Administrative Services Agreement, dated January 24, 2008, between Northwest Pipeline GP and Northwest Pipeline Services LLC (filed on January 30, 2008 as Exhibit 10.1 to our current report on Form 8-K (File No. 001-07414) and incorporated herein by reference).
10.2	Assignment Agreement dated February 13, 2013, by and between Northwest Pipeline Services LLC and Williams WPC-I, LLC, effective January 1, 2013 (filed on February 3, 2015 as Exhibit 10(b) to our annual report on Form 10-K (File No. 001-07414) and incorporated herein by reference).
10.3	Amended and Restated Credit Agreement dated as of October 8, 2021 between The Williams Companies, Inc., Northwest Pipeline LLC, and Transcontinental Gas Pipeline Company, LLC, as borrowers, the lenders named therein, and Wells Fargo Bank, National Association, as Administrative Agent (filed on October 8, 2021 as Exhibit 10.1 to The Williams Companies, Inc.’s current report on Form 8-K (File No. 001-04174) and incorporated herein by reference).
31.1*	Certification of Principal Executive Officer pursuant to Rules 13a-14(a) and 15d-14(a) promulgated under the Securities Exchange Act of 1934, as amended and Item 601(b)(31) of Regulation S-K, as adopted pursuant to Section 302 of The Sarbanes-Oxley Act of 2002.
31.2*	Certification of Principal Financial Officer pursuant to Rules 13a-14(a) and 15d-14(a) promulgated under the Securities Exchange Act of 1934, as amended, and Item 601(b)(31) of Regulation S-K, as adopted pursuant to Section 302 of The Sarbanes-Oxley Act of 2002.
32**	Certification of Principal Executive Officer and Principal Financial Officer pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002.
101.INS*	XBRL Instance Document. The instance document does not appear in the Interactive Data File because its XBRL tags are embedded within the inline XBRL document.
101.SCH*	XBRL Taxonomy Extension Schema.
101.CAL*	XBRL Taxonomy Extension Calculation Linkbase.
101.DEF*	XBRL Taxonomy Definition Linkbase
101.LAB*	XBRL Taxonomy Extension Label Linkbase.
101.PRE*	XBRL Taxonomy Extension Presentation Linkbase.
104*	Cover Page Interactive Data File. The cover page interactive data file does not appear in the interactive data file because its XBRL tags are embedded within the inline XBRL document (contained in Exhibit 101).

* Filed herewith

** Furnished herewith

50

Item 16. Form 10-K Summary

Not applicable.

51

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

NORTHWEST PIPELINE LLC
(Registrant)
By:	/s/ Billeigh W. Mark
	Billeigh W. Mark
	Controller

Date: February 21, 2024

Pursuant to the requirements of the Securities Exchange Act of 1934, this report has been signed below by the following persons on behalf of the registrant in the capacities and on the dates indicated.

Signature	Title
/s/ Chad A. Teply	Management Committee Member and Senior Vice President (Principal Executive Officer)
Chad A. Teply
/s/ Mary A. Hausman	Vice President and Chief Accounting Officer (Principal Financial Officer)
Mary A. Hausman
/s/ Billeigh W. Mark	Controller (Principal Accounting Officer)
Billeigh W. Mark

Date: February 21, 2024

EX-31.1

Exhibit 31.1

SECTION 302 CERTIFICATION

I, Chad A. Teply, certify that:

1.I have reviewed this annual report on Form 10-K of Northwest Pipeline LLC;

2.Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report; 

3.Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4.The registrant’s other certifying officer(s) and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

(a)Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

(b)Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

(c)Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

(d)Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5.The registrant’s other certifying officer(s) and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

(a)All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

(b)Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: February 21, 2024

By:	/s/ Chad A. Teply
	Chad A. Teply
	Senior Vice President
	(Principal Executive Officer)

EX-31.2

Exhibit 31.2

SECTION 302 CERTIFICATION

I, Mary A. Hausman, certify that:

1.I have reviewed this annual report on Form 10-K of Northwest Pipeline LLC;

2.Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report; 

3.Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4.The registrant’s other certifying officer(s) and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

(a)Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

(b)Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

(c)Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

(d)Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5.The registrant’s other certifying officer(s) and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

(a)All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

(b)Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: February 21, 2024

By:	/s/ Mary A. Hausman
	Mary A. Hausman
	Vice President and Chief Accounting Officer
	(Principal Financial Officer)

EX-32

Exhibit 32

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Annual Report of Northwest Pipeline LLC (the “Company”) on Form 10-K for the period ending December 31, 2023 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), each of the undersigned hereby certifies, in his capacity as an officer of the Company, pursuant to 18 U.S.C. §1350, as adopted pursuant to §906 of the Sarbanes-Oxley Act of 2002, that to his knowledge:

(1)The Report fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2)The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/ Chad A. Teply

Chad A. Teply

Senior Vice President

February 21, 2024

/s/ Mary A. Hausman

Mary A. Hausman

Vice President and Chief Accounting Officer

February 21, 2024

A signed original of this written statement required by Section 906 has been provided to, and will be retained by, the Company and furnished to the Securities and Exchange Commission or its staff upon request.

The foregoing certification is being furnished to the Securities and Exchange Commission as an exhibit to the Report and shall not be considered filed as part of the Report.

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	Dec. 31, 2023	Feb. 21, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
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Entity Registrant Name	Northwest Pipeline LLC
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Entity Address, Address Line One	One Williams Center
Entity Address, City or Town	Tulsa
Entity Address, State or Province	OK
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Audit Information	12 Months Ended
	Dec. 31, 2023
Audit Information [Abstract]
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Statement of Net Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Revenue
Operating revenues	$ 439,858	$ 447,335	$ 443,558
Operating Expenses:
Operation and maintenance	88,005	84,260	76,016
General and administrative	50,524	51,682	49,204
Depreciation and amortization	111,434	114,384	113,180
Taxes, other than income taxes	12,297	17,039	16,836
Regulatory charges resulting from tax rate changes	0	19,621	23,580
Other (income) expense, net	(16,519)	1,712	1,449
Total operating expenses	245,741	288,698	280,265
Operating Income	194,117	158,637	163,293
Other (Income) and Other Expenses:
Interest expense	27,863	30,987	29,986
Allowance for equity and borrowed funds used during construction (AFUDC)	(3,846)	(2,950)	(1,606)
Miscellaneous other (income) expense, net	(9,619)	(6,174)	(595)
Total other (income) and other expenses	14,398	21,863	27,785
Net Income	179,719	136,774	135,508
Natural gas transportation
Operating Revenue
Operating revenues	414,647	429,526	428,136
Natural gas storage
Operating Revenue
Operating revenues	15,298	13,104	12,883
Other
Operating Revenue
Operating revenues	$ 9,913	$ 4,705	$ 2,539

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Balance Sheet - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current Assets:
Cash	$ 0	$ 0
Receivables:
Trade	39,080	39,746
Other	1,485	606
Materials and supplies, at average cost	7,759	8,925
Exchange gas receivables	3,165	35,851
Regulatory assets	2,054	13,565
Other	1,801	3,627
Total current assets	214,495	414,790
Property, plant and equipment	3,974,900	3,836,254
Less-Accumulated depreciation and amortization	2,026,007	1,941,806
Total property, plant and equipment, net	1,948,893	1,894,448
Other Long-Term Assets:
Regulatory assets	35,796	15,951
Right-of-use assets	8,725	9,621
Deferred charges and other	19,450	15,167
Total other assets	63,971	40,739
Total assets	2,227,359	2,349,977
Payables:
Trade	47,822	25,761
Accrued liabilities:
Exchange gas payables	5,553	42,451
Regulatory liabilities	21,374	145,243
Taxes, other than income taxes	7,388	10,853
Interest	5,505	5,505
Customer advances	5,016	4,415
Other	10,588	4,011
Total current liabilities	116,026	250,354
Long-Term Debt	581,178	580,083
Other Long-Term Liabilities:
Regulatory liabilities	252,272	271,706
Asset retirement obligations	136,263	129,306
Lease liability	7,193	7,857
Other	1,231	2,394
Total other long-term liabilities	396,959	411,263
Contingent Liabilities and Commitments (Note 5)
Member's Equity:
Member’s capital	1,073,892	1,073,892
Retained earnings	59,304	34,385
Total member’s equity	1,133,196	1,108,277
Total liabilities and member’s equity	2,227,359	2,349,977
Related Party [Member]
Receivables:
Advances to affiliate	157,776	310,641
Affiliates	1,375	1,829
Payables:
Affiliates	$ 12,780	$ 12,115

XML

Statement of Changes in Member's Equity - USD ($) $ in Thousands	Total	Member's Capital	Retained Earnings
Balance at beginning of period at Dec. 31, 2020		$ 1,073,892	$ 66,503
Net income	$ 135,508		135,508
Cash distributions to parent	(166,500)		(166,500)
Balance at end of period at Dec. 31, 2021	1,109,403	1,073,892	35,511
Net income	136,774		136,774
Cash distributions to parent	(137,900)		(137,900)
Balance at end of period at Dec. 31, 2022	1,108,277	1,073,892	34,385
Net income	179,719		179,719
Cash distributions to parent	(154,800)		(154,800)
Balance at end of period at Dec. 31, 2023	$ 1,133,196	$ 1,073,892	$ 59,304

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Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
OPERATING ACTIVITIES:
Net income	$ 179,719	$ 136,774	$ 135,508
Adjustments to reconcile net cash provided (used) by operating activities:
Depreciation and amortization	111,434	114,384	113,180
Regulatory charges resulting from tax rate changes	0	19,621	23,580
Allowance for equity funds used during construction (equity AFUDC)	(3,155)	(2,335)	(1,360)
Changes in current assets and liabilities:
Trade and other accounts receivable	(213)	(515)	(1,632)
Affiliate receivables	454	(1,457)	(321)
Materials and supplies	1,166	(16)	898
Regulatory assets	(340)	(445)	111
Other current assets	1,432	(345)	(221)
Trade accounts payable	4,295	(1,230)	(3,571)
Affiliate payables	665	(1,025)	9,030
Regulatory liabilities	(125,502)	145,242	2
Other accrued liabilities	3,021	1,361	(877)
Regulatory assets	(28,813)	0	0
Regulatory liabilities	(19,530)	(140,190)	4,374
Other, net	4,615	(1,182)	(5,739)
Net cash provided (used) by operating activities	129,248	268,642	272,962
FINANCING ACTIVITIES:
Cash distributions to parent	(154,800)	(137,900)	(166,500)
Net cash provided (used) by financing activities	(154,800)	(137,900)	(166,500)
Property, plant and equipment:
Capital expenditures	(124,932)	(106,729)	(78,787)
Contributions and advances for construction costs	(6,066)	(10,555)	(10,268)
Disposal of property, plant and equipment, net	(8,447)	(5,369)	(4,370)
Advances to affiliate, net	152,865	(29,199)	(33,573)
Net cash provided (used) in investing activities	25,552	(130,742)	(106,462)
Increase (decrease) in cash	0	0	0
Cash at beginning of period	0	0	0
Supplemental Cash Flow Elements [Abstract]
Increases to property, plant and equipment, exclusive of equity AFUDC	(139,620)	(109,359)	(88,791)
Changes in related accounts payable and accrued liabilities	14,688	2,630	10,004
Capital expenditures	(124,932)	(106,729)	(78,787)
Cash at end of period	$ 0	$ 0	$ 0

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Summary of Significant Accounting Policies (Notes)

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

Corporate Structure and Control

In this report, Northwest Pipeline LLC (Northwest) is at times referred to in the first person as “we,” “us” or “our.”

Northwest is indirectly owned by The Williams Companies, Inc. (Williams), a publicly traded Delaware corporation. Northwest is a single member limited liability company, and as such, single member losses are limited to the amount of its investment.

Nature of Operations

We own and operate an interstate pipeline system for the mainline transmission of natural gas. This system extends from the San Juan Basin in northwestern New Mexico and southwestern Colorado through Colorado, Utah, Wyoming, Idaho, Oregon and Washington to a point on the Canadian border near Sumas, Washington.

Summary of Significant Accounting Policies

Use of Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates.

Significant estimates and assumptions include:

•Litigation-related contingencies;

•Environmental remediation obligations;

•Impairment assessments of long-lived assets;

•Depreciation;

•Asset retirement obligations; and

•Measurement of regulatory assets and liabilities.

These estimates are discussed further throughout these notes.

Regulatory Accounting

We are regulated by the Federal Energy Regulatory Commission (FERC). Accounting Standards Codification (ASC) Topic 980, “Regulated Operations,” (Topic 980), provides that certain costs that would otherwise be charged to expense should be deferred as regulatory assets, based on the expected recovery from customers in future rates. Likewise, certain actual or anticipated credits that would otherwise reduce expense should be deferred as regulatory liabilities, based on the expected return to customers in future rates. Management's expected recovery of deferred costs and return of deferred credits generally results from specific decisions by regulators granting such ratemaking treatment. We record certain incurred costs and obligations as regulatory assets or liabilities if, based on regulatory orders or other available evidence, it is probable that the costs or obligations will be included in amounts allowable for recovery or refunded in future rates. Accounting for businesses that are regulated and apply the provisions of Topic 980 can differ from the accounting requirements for non-regulated businesses. Transactions that are recorded differently as a result of regulatory accounting requirements include the capitalization of an equity return component on regulated capital projects, capitalization of other project costs, retirements of general plant assets, levelized cost of service, negative salvage, asset retirement obligations (ARO), employee-related benefits, environmental costs, and other costs and taxes included in, or expected to be included in, future rates. As a rate-regulated entity, our management has determined that it is appropriate to apply the accounting prescribed by Topic 980, and, accordingly, the

accompanying financial statements include the effects of the types of transactions described above that result from regulatory accounting requirements.

Revenue Recognition

Our customers are comprised of public utilities, municipalities, direct industrial users, electric power generators, and natural gas marketers and producers.

Service revenue contracts from our gas pipeline business contain a series of distinct services, with the majority of our contracts having a single performance obligation that is satisfied over time as the customer simultaneously receives and consumes the benefits provided by our performance.

Certain customers reimburse us for costs we incur associated with construction of property, plant, and equipment utilized in our operations. As a rate-regulated entity applying Topic 980, we follow FERC guidelines with respect to reimbursement of construction costs. FERC tariffs only allow for cost reimbursement and are non-negotiable in nature; thus, in our judgment, the construction activities do not represent an ongoing major and central operation of our gas pipeline business and are not within the scope of ASC Topic 606, “Revenues from Contracts with Customers.” Accordingly, cost reimbursements are treated as a reduction to the cost of the constructed asset.

Operating Revenues

We are subject to regulation by certain state and federal authorities, including the FERC, with revenue derived from both firm and interruptible transportation and storage contracts. Firm transportation and storage agreements provide for a fixed reservation charge based on the pipeline or storage capacity reserved, and a commodity charge based on the volume of natural gas delivered/stored, each at rates specified in our FERC tariffs or as negotiated with our customers, with contract terms that are generally long-term in nature. Most of our long-term contracts contain an evergreen provision, which allows the contracts to be extended for periods primarily up to one year in length an indefinite number of times following the specified contract term and until terminated generally by either us or the customer, but in certain cases unilaterally by the customer, with advance notice of termination ranging from one to five years. Interruptible transportation and storage agreements provide for a volumetric charge based on actual commodity transportation or storage utilized in the period in which those services are provided, and the contracts are generally limited to one-month periods or less. Our performance obligations include the following:

•Firm transportation or storage under firm transportation and storage contracts—an integrated package of services typically constituting a single performance obligation, which includes standing ready to provide such services and receiving, transporting or storing (as applicable), and redelivering commodities;

•Interruptible transportation and storage under interruptible transportation and storage contracts—an integrated package of services typically constituting a single performance obligation once scheduled, which includes receiving, transporting or storing (as applicable), and redelivering commodities.

In situations where, in our judgment, we consider the integrated package of services as a single performance obligation, which represents a majority of our contracts with customers, we do not consider there to be multiple performance obligations because the nature of the overall promise in the contract is to stand ready (with regard to firm transportation and storage contracts), receive, transport or store, and redeliver natural gas to the customer; therefore, revenue is recognized over time upon satisfaction of our daily stand ready performance obligation.

We recognize revenues for reservation charges over the performance obligation period, which is the contract term, regardless of the volume of natural gas that is transported or stored. Revenues for commodity charges from both firm and interruptible transportation services and storage services are recognized when natural gas is delivered at the agreed upon point or when natural gas is injected or withdrawn from the storage facility because they specifically relate to our efforts to provide these distinct services. Generally, reservation charges and commodity charges are recognized as revenue in the same period they are invoiced to our customers. As a result of the ratemaking process, certain amounts collected by us may be subject to refunds upon the issuance of final orders by the FERC in pending rate proceedings. We use judgment to record estimates of rate refund liabilities considering our and other third-party regulatory proceedings, advice of counsel, and other risks. At December 31, 2023 and 2022, we had no such rate refund liabilities.

In the course of providing transportation services to customers, we may receive different quantities of natural gas from customers than the quantities delivered on behalf of those customers or consumed in fuel to operate our system. The resulting

customer imbalances are typically settled through the receipt or delivery of gas in the future based on the timelines outlined in Northwest’s tariff, whereas the over/under recovery of fuel is cleared up through Northwest’s semi-annual fuel tracker. Customer imbalances to be repaid or recovered in-kind are recorded as Exchange gas receivables or Exchange gas payables in our Balance Sheet. The under recovery of fuel is recorded as a Regulatory Asset and the over recovery is recorded as a Regulatory Liability. These imbalances are valued at published spot rates.

Contract Assets

Our contract assets consist of discounts provided to customers in the beginning of the contract term that are recognized on a straight-line basis over the entire contract term resulting in revenue recognition occurring prior to actual billings. Contract assets are included within Other on our Balance Sheet.

Contract Liabilities

Our contract liabilities consist of a fixed rate facility charge billed to customers that declines annually as specified per the tariff. These liabilities are classified as current or non-current according to when such amounts are expected to be recognized. Current and non-current liabilities are included within Accrued Liabilities and Other Long-Term Liabilities, respectively, on our Balance Sheet.

Leases

We are a lessee through noncancellable lease agreements for property and equipment consisting primarily of buildings, land, vehicles, and equipment used in both our operations and administrative functions. We recognize a lease liability with an offsetting right-of-use asset in our Balance Sheet for operating leases based on the present value of the future lease payments. We have elected to combine lease and nonlease components for all classes of leased assets in our calculation of the lease liability and the offsetting right-of-use asset.

Our lease agreements require both fixed and variable periodic payments, with initial terms typically ranging from one year to 30 years. Payment provisions in certain of our lease agreements contain escalation factors which may be based on stated rates or a change in a published index at a future time. The amount by which a lease escalates based on the change in a published index, which is not known at lease commencement, is considered a variable payment and is not included in the present value of the future lease payments, which only includes those that are stated or can be calculated based on the lease agreement at lease commencement. In addition to the noncancellable periods, many of our lease agreements provide for one or more extensions of the lease agreement for periods ranging from one year in length to an indefinite number of times following the specified contract term. Other lease agreements provide for extension terms that allow us to utilize the identified leased asset for an indefinite period of time so long as the asset continues to be utilized in our operations. In consideration of these renewal features, we assess the term of the lease agreements, which includes using judgment in the determination of which renewal periods and termination provisions, when at our sole election, will be reasonably certain of being exercised. Periods after the initial term or extension terms that allow for either party to the lease to cancel the lease are not considered in the assessment of the lease term. Additionally, we have elected to exclude leases with an original term of one year or less, including renewal periods, from the calculation of the lease liability and the offsetting right-of-use asset.

We use judgment in determining the discount rate upon which the present value of the future lease payments is determined. This rate is based on a collateralized interest rate corresponding to the term of the lease agreement using company, industry, and market information available.

Environmental Matters

We are subject to federal, state, and local environmental laws and regulations. Environmental expenditures are expensed or capitalized depending on their economic benefit and potential for rate recovery. We believe that expenditures required to meet applicable environmental laws and regulations are prudently incurred in the ordinary course of business and such expenditures would be permitted to be recovered through rates.

Greenhouse Gas Emission Allowances

In accordance with the Climate Commitment Act of the state of Washington, which established a market-based cap-and-invest program, we are required to obtain emission allowances for the carbon emissions from nine of our thirteen compressor stations within the state of Washington whose annual carbon emissions exceed 25,000 metric tons of carbon dioxide equivalent. We record the purchased emission allowances at cost and the associated accumulated interest to a regulatory asset. The difference between the allowances held and the allowances required based on actual emissions for the period are measured using an estimate based on our most recent cost of allowances and accrued to a current liability and to a regulatory asset. Our Settlement allows us to recover the costs of purchasing allowances under the program in our next rate case.

Property, Plant, and Equipment

Property, plant and equipment, consisting principally of natural gas transmission facilities, is recorded at cost. The FERC identifies installation, construction and replacement costs that are to be capitalized and included in our asset base for recovery in rates. Routine maintenance, repairs, and renewal costs are charged to income as incurred. Gains or losses from the ordinary sale or retirement of property, plant and equipment are charged or credited to accumulated depreciation; certain other gains or losses are recorded in operating income.

We provide for depreciation under the composite (group) method at straight-line FERC prescribed rates that are applied to the cost of the group for transmission and storage facilities. Under this method, assets with similar lives and characteristics are grouped and depreciated as one asset. Included in our depreciation rates is a negative salvage component (net cost of removal) that we currently collect in rates. Our depreciation rates are subject to change each time we file a general rate case with the FERC.

The following table presents Total property, plant and equipment, net as presented on the Balance Sheet:

	Depreciation Rate	December 31,
		2023		2022
		(Thousands)
Transmission facilities	2.70%  -  10.20%	$	3,569,545	$	3,490,141
Storage facilities	1.60%  -  2.76%	155,433		142,326
Construction in progress	Not applicable	84,945		44,702
Other	0% - 33.33%	164,977		159,085
Property, plant and equipment		3,974,900		3,836,254
Less-Accumulated depreciation and amortization		2,026,007		1,941,806
Total property, plant and equipment, net		$	1,948,893	$	1,894,448

We record a liability and increase the basis in the underlying asset for the present value of each expected future ARO at the time the liability is initially incurred, typically when the asset is acquired or constructed. Measurement of ARO includes, as a component of future expected costs, an estimate of the price that a third party would demand, and could expect to receive, for bearing the uncertainties inherent in the obligations, sometimes referred to as market-risk premium. We measure changes in the liability due to passage of time by applying an interest method of allocation. This amount is recognized as an increase in the carrying amount of the liability and is offset by a regulatory asset. The gross regulatory asset balances associated with ARO as of December 31, 2023 and 2022 were $116.2 million and $109.0 million, respectively. The regulatory asset is expected to be fully recovered through the negative salvage component of depreciation included in our rates; as such, that amount of the negative salvage component of accumulated depreciation has been reclassified and netted against the amount of the ARO regulatory asset to result in a regulatory liability of $30.7 million and $30.6 million at December 31, 2023 and 2022, respectively.

Allowance for Funds Used During Construction

Allowance for funds used during construction (AFUDC) represents the estimated cost of borrowed and equity funds applicable to utility plant in process of construction and is included as a cost of property, plant and equipment because it

constitutes an actual cost of construction under established regulatory practices. The FERC has prescribed a formula to be used in computing separate allowances for borrowed and equity AFUDC. The allowance for borrowed funds used during construction was $0.7 million for 2023, $0.7 million for 2022, and $0.2 million for 2021. The allowance for equity funds was $3.1 million, $2.3 million, and $1.4 million for 2023, 2022, and 2021, respectively.

Income Taxes

We are a natural gas company organized as a pass-through entity and our taxable income or loss is consolidated on the federal income tax return of our parent, Williams. We generally are treated as a pass-through entity for state and local income tax purposes, and those taxes are generally borne on a consolidated basis by Williams. Net income for financial statement purposes may differ significantly from taxable income of Williams as a result of differences between the tax basis and financial reporting basis of assets and liabilities.

Accounts Receivable

Accounts receivable are carried on a gross basis less an allowance for doubtful accounts. We estimate the allowance for doubtful accounts, considering current expected credit losses using a forward-looking “expected loss” model, the financial condition of our customers, and the age of past due accounts. The majority of our trade receivable balances are due within 30 days. We monitor the credit quality of our counterparties through review of collection trends, credit ratings, and other analyses, such as bankruptcy monitoring, if applicable. Financial assets are evaluated as one pool. Changes in counterparty risk factors could lead to reassessment of the composition of our financial assets as one pool. We calculate our allowance for credit losses incorporating an aging method. In estimating our expected credit losses, we utilized historical loss rates over many years. Our expected credit loss estimate considered both internal and external forward-looking commodity price expectations, as well as counterparty credit ratings, and factors impacting their near-term liquidity.

We do not offer extended payment terms and typically receive payment within one month. We consider receivables past due if full payment is not received by the contractual due date. Past due accounts are generally written off against the allowance for doubtful accounts only after all collection attempts have been exhausted. We do not have a material amount of significantly aged receivables at December 31, 2023 and 2022.

Materials and Supplies Inventory

All materials and supplies inventory is stated at average cost. We perform an annual review of materials and supplies inventories, including a quarterly analysis of parts that may no longer be useful due to planned replacements of compressor engines and other components on our system. Based on this assessment, we record a reserve for the value of the inventory which can no longer be used for maintenance and repairs on our pipeline. The reserve for inventory was $1.0 million at December 31, 2023, and there was a minimal reserve at December 31, 2022.

Contingent Liabilities

We record liabilities for estimated loss contingencies, including environmental matters, when we assess that a loss is probable and the amount of the loss can be reasonably estimated. These liabilities are calculated based upon our assumptions and estimates with respect to the likelihood or amount of loss and upon advice of legal counsel, engineers, or other third-parties regarding the probable outcomes of the matters. These calculations are made without consideration of any potential recovery from third-parties. We recognize insurance recoveries or reimbursements from others when realizable. Revisions to these liabilities are generally reflected in income when new or different facts or information become known or circumstances change that affect the previous assumptions or estimates.

Pension and Other Postretirement Benefits

We do not have employees. Certain of the costs charged to us by Williams associated with employees who directly support us include costs related to Williams’ pension and other postretirement benefit plans (see Note 7 – Benefit Plans). Although the underlying benefit plans of Williams are single-employer plans, we follow multiemployer plan accounting whereby the amount charged to us, and thus paid by us, is based on our share of net periodic benefit cost.

Cash Flows from Operating Activities

We use the indirect method to report cash flows from operating activities, which requires adjustments to net income to reconcile to net cash flows provided by operating activities.

Interest Payments

Cash payments for interest, net of interest capitalized, were $26.1 million in 2023, 2022 and 2021.

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Revenue Recognition (Notes)

12 Months Ended

Dec. 31, 2023

Revenue Recognition [Abstract]

Revenue from Contract with Customer [Text Block]

Revenue Recognition

Revenue by Category

Our revenue disaggregation by major service line includes Natural gas transportation, Natural gas storage, and Other, which are separately presented on the Statement of Net Income.

Contract Assets

The following table presents a reconciliation of our contract assets:

	Year Ended December 31,
	2023		2022
	(Thousands)
Balance at beginning of period	$	12,490	$	7,943
Revenue recognized in excess of amounts invoiced	4,316		4,547
Balance at end of period	$	16,806	$	12,490

Contract Liabilities

The following table presents a reconciliation of our contract liabilities:

	Year Ended December 31,
	2023		2022
	(Thousands)
Balance at beginning of period	$	2,643	$	3,672
Recognized in revenue	(1,175)		(1,029)
Balance at end of period	$	1,468	$	2,643

Remaining Performance Obligations

Our remaining performance obligations primarily include reservation charges on contracted capacity on our firm transportation and storage contracts with customers. Amounts from certain contracts included in the table below, which are subject to periodic review and approval by the FERC, reflect the rates for such services in our current FERC tariffs for the life of the related contracts; however, these rates may change based on future rate cases or settlements approved by the FERC. This table excludes the variable consideration component for commodity charges. Certain of our contracts contain evergreen and other renewal provisions for periods beyond the initial term of the contract. The remaining performance obligations as of December 31, 2023, do not consider potential future performance obligations for which the renewal has not been exercised and exclude contracts with customers for which the underlying facilities have not received FERC authorization to be placed into service.

The following table presents the amount of the contract liabilities balance expected to be recognized as revenue when performance obligations are satisfied and the transaction price allocated to the remaining performance obligations under certain contracts as of December 31, 2023.

	Contract Liabilities		Remaining Performance Obligations
	(Thousands)
2024 (one year)	$	1,178	$	386,252
2025 (one year)	290		369,844
2026 (one year)	—		354,605
2027 (one year)	—		351,285
2028 (one year)	—		345,753
Thereafter	—		2,228,679
Total	$	1,468	$	4,036,418

Accounts Receivable

Receivables from contracts with customers are included within Receivables - Trade and Receivables - Affiliates and receivables that are not related to contracts with customers are included within the balance of Receivables - Advances to affiliate and Receivables - Other in our Balance Sheet.

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Leases (Notes)

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Leases of Lessee Disclosure [Text Block]

Leases

We are a lessee through non-cancellable lease agreements for property and equipment consisting primarily of buildings, land, vehicles, and equipment used in both our operations and administrative functions.

	Year Ended December 31,
	2023		2022		2021
	(Thousands)
Lease Cost:
Operating lease cost	$	1,205	$	1,226		$	1,334
Variable lease cost	588		578			681
Total lease cost	$	1,793	$	1,804		$	2,015
Cash paid for operating lease liabilities	$	954	$	950		$	2,395
			December 31,
			2023			2022
			(Thousands)
Other Information:
Right-of-use assets			$	8,725		$	9,621
Operating lease liabilities:
Current (included in Accrued liabilities - Other on our Balance Sheet)			$	701		$	681
Lease liability			$	7,193		$	7,857
Weighted-average remaining lease term - operating leases (years)			15			16
Weighted-average discount rate - operating leases			4.18%			4.12%

As of December 31, 2023, the following table represents our operating lease maturities, including renewal provisions that we have assessed as being reasonably certain of exercise, for each of the years ended December 31:

	(Thousands)
2024	$	954
2025	971
2026	973
2027	987
2028	961
Thereafter	6,651
Total future lease payments	11,497
Less amount representing interest	3,603
Total obligations under operating leases	$	7,894

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Rate and Regulatory Matters (Notes)

12 Months Ended

Dec. 31, 2023

Regulated Operations [Abstract]

Public Utilities, Disclosure of Rate Matters [Text Block]

Rate and Regulatory Matters

Rate Case Settlement

On November 15, 2022, the FERC approved our Petition for Approval of Pre-Filing Stipulation and Settlement Agreement (Settlement) in Docket No. RP22-1155. The Settlement establishes a new general system firm Rate Schedule TF-1 (Large Customer) daily reservation rate of $0.37250/Dth with a $0.00935/Dth commodity rate (which were made effective January 1, 2023), resolved other rate issues, established a Modernization and Emission Reduction Program and satisfies our rate case filing obligation under our settlement in Docket No. RP17-346.

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Contingent Liabilities and Commitments (Notes)

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Contingent Liabilities and Commitments

Contingent Liabilities and Commitments

Environmental Matters

Beginning in the mid-1980s, we evaluated many of our facilities for the presence of toxic and hazardous substances to determine to what extent, if any, remediation might be necessary. We identified polychlorinated biphenyl (PCB) contamination in air compressor systems, soils, and related properties at certain compressor station sites. Similarly, we identified hydrocarbon impacts at these facilities due to the former use of earthen pits, lubricating oil leaks or spills, and excess pipe coating released to the environment. In addition, heavy metals have been identified at these sites due to the former use of mercury containing meters and paint and welding rods containing lead, cadmium, and arsenic. The PCBs were remediated pursuant to a Consent Decree with the U.S. Environmental Protection Agency (EPA) in the late 1980s, and we conducted a voluntary clean-up of the hydrocarbon and mercury impacts in the early 1990s. In 2005, the Washington Department of Ecology required us to re-evaluate our previous clean-ups in Washington. During 2006 to 2015, 129 meter stations were evaluated, of which 82 required remediation. As of December 31, 2023, two meter stations are still being remediated. During 2006 to 2018, 14 compressor stations were evaluated, of which 11 required remediation. As of December 31, 2023, four compressor stations are still being remediated. At December 31, 2023, we had accrued liabilities totaling approximately $1.0 million, $0.2 million of which is recorded in Accrued liabilities - Other and $0.8 million of which is recorded in Other Long-Term Liabilities - Other on the Balance Sheet. At December 31, 2022, we had accrued liabilities totaling approximately $1.0 million, $0.1 million of which is recorded in Accrued liabilities - Other and $0.9 million of which is recorded in Other Long-Term Liabilities - Other on the Balance Sheet. We are conducting environmental assessments and implementing a variety of remedial measures that may result in increases or decreases in the total estimated costs.

The EPA and various state regulatory agencies routinely propose and promulgate new rules, and issue updated guidance to existing rules. These rulemakings include, but are not limited to, rules for reciprocating internal combustion engine and

combustion turbine maximum achievable control technology, review and updates to the National Ambient Air Quality Standards, and rules for new and existing source performance standards for volatile organic compounds and methane. We continuously monitor these regulatory changes and how they may impact our operations. Implementation of new or modified regulations may result in impacts to our operations and increase the cost of additions to Total property, plant, and equipment, net on the Balance Sheet for both new and existing facilities in affected areas; however, due to regulatory uncertainty on final rule content and applicability timeframes, we are unable to reasonably estimate the cost of these regulatory impacts at this time.

Environmental expenditures are expensed or capitalized depending on their future economic benefit and potential for rate recovery. We believe that, with respect to any expenditures required to meet applicable standards and regulations, the FERC would grant the requisite rate relief so that substantially all of such expenditures would be permitted to be recovered through rates.

Washington State Climate Commitment Act

In 2021, the state of Washington passed its Climate Commitment Act establishing a market-based cap-and-invest program to reduce carbon emissions. This program took effect on January 1, 2023, and sets a limit, or cap, on overall carbon emissions in the state and requires businesses like ours to obtain allowances equal to their annual covered carbon emissions. The state’s cap will be reduced over time to meet the state’s carbon emissions reduction targets, which means fewer carbon emissions allowances will be available to purchase each year. These allowances can be purchased through quarterly auctions hosted by the state or bought and sold on a secondary market. In 2023, we began purchasing allowances for the carbon emissions from nine of our thirteen compressor stations within the state whose annual carbon emissions exceed 25,000 metric tons of carbon dioxide equivalent. We also began purchasing allowances for our delivery of natural gas to certain of our customers and certain of our facilities in the state whose annual carbon emissions are insufficient to require their direct participation in the program. Our Settlement allows us to recover the costs of purchasing allowances under the program in our next rate case.

As of December 31, 2023 a total of $22.3 million was included in Other Assets - Regulatory assets on our Balance Sheet and was comprised of the cost of the purchased allowances held, the estimated difference between the allowances held and the allowances required, and the interest income component of the regulatory asset. At December 31, 2023, $3.7 million was included in Accrued liabilities - Other on our Balance Sheet as the estimated difference. The interest income is reflected in Miscellaneous other (income) expense, net on our Statement of Net Income and was $0.6 million for the year ended December 31, 2023.

Other Matters

Various other proceedings are pending against us and are considered incidental to our operations.

Summary

We have disclosed all significant matters for which we are unable to reasonably estimate a range of possible loss. We estimate that for all matters for which we are able to reasonably estimate a range of loss, including those noted above and others that are not individually significant, our aggregate reasonably possible losses beyond amounts accrued for all of our contingent liabilities are immaterial to our expected future annual results of operations, liquidity and financial position. These calculations have been made without consideration of any potential recovery from third-parties.

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Debt and Financing Arrangements [Notes]

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Debt Disclosure

Debt and Financing Arrangements

Long-Term Debt 

	December 31,
	2023		2022
	(Thousands)
7.125% Debentures due 2025	$	85,000	$	85,000
4.0% Notes due 2027	500,000		500,000
Unamortized debt issuance costs	(1,954)		(2,517)
Unamortized debt discount	(1,868)		(2,400)
Total long-term debt	$	581,178	$	580,083

The following table reflects future maturities of long-term (at face value) debt for the next five years (in thousands):

2025	$	85,000
2027	$	500,000

No property is pledged as collateral under any of our long-term debt.

Credit Facility

In October 2021, we along with Williams and Transcontinental Gas Pipe Line Company, LLC (Transco), the lenders named therein, and an administrative agent entered into an amended and restated credit agreement (Credit Agreement) that reduced aggregate commitments available from $4.5 billion to $3.75 billion, with up to an additional $500 million increase in aggregate commitments available under certain circumstances. The Credit Agreement was effective on October 8, 2021. In the second quarter of 2023, the maturity date of our Credit Agreement was extended one year and now expires October 8, 2027. The amended Credit Agreement allows the co-borrowers to request up to two extensions of the maturity date each for an additional one-year period to allow a maturity date as late as October 8, 2029, under certain circumstances. Additionally, the amended Credit Agreement replaces the London Interbank Offered Rate with the Term Secured Overnight Financing Rate as the benchmark interest rate index. The Credit Agreement allows for swing line loans up to an aggregate of $200 million, subject to available capacity under the credit facility, and letters of credit commitments of $500 million. We and Transco are each able to borrow up to $500 million under this credit facility to the extent not otherwise utilized by the other co-borrowers. At December 31, 2023, no letters of credit have been issued and no loans to Williams were outstanding under the credit facility.

The Credit Agreement contains the following terms and conditions:

•Various covenants may limit, among other things, a borrower’s and its material subsidiaries’ ability to grant certain liens supporting indebtedness, merge or consolidate, sell all or substantially all of its assets in certain circumstances, make certain distributions during an event of default, and each borrower and each borrower’s respective material subsidiaries’ ability to enter into certain restrictive agreements.

•If an event of default with respect to a borrower occurs under the credit facility, the lenders will be able to terminate the commitments for the respective borrowers and accelerate the maturity of the loans of the defaulting borrower under the credit facility and exercise other rights and remedies.

•Other than swing line loans, each time funds are borrowed, the applicable borrower may choose from two methods of calculating interest: a fluctuating base rate equal to an alternative base rate as defined in the Credit Agreement plus an applicable margin or a periodic fixed rate equal to the Term Secured Overnight Financing Rate plus an applicable margin. Williams is required to pay a commitment fee based on the unused portion of the credit facility. The applicable margin is determined by reference to a pricing schedule based on the applicable borrower’s senior unsecured long-term debt ratings and the commitment fee is determined by reference to a pricing schedule based on Williams’ senior unsecured long-term debt ratings.

The ratio of debt to capitalization (defined as net worth plus debt), each as defined in the Credit Agreement, must be no greater than 65 percent for each of Transco and Northwest.

Commercial Paper Program

Williams has a $3.5 billion commercial paper program. Williams’ management considers amounts outstanding under this program to be a reduction of available capacity under the credit facility. At December 31, 2023, Williams had $725 million of commercial paper outstanding, which was paid down in January 2024.

Restrictive Debt Covenants

At December 31, 2023, none of our debt instruments restrict the amount of distributions to our parent, provided, however, that under the credit facility described above, we are restricted from making distributions to our parent during an event of default if we have directly incurred indebtedness under the credit facility. Our debt agreements contain restrictions on our ability to incur secured debt beyond certain levels. At December 31, 2023, we were in compliance with the covenants contained in our credit agreements and indentures.

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Benefit Plans (Notes)

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

Employee Benefit Plans [Text Block]

Benefit Plans

Certain of the benefit costs charged to us by Williams associated with employees who directly support us are described below. Additionally, allocated corporate expenses from Williams to us also include amounts related to these same employee benefits, which are not included in the amounts presented below (see Note 9 – Transactions With Major Customers and Affiliates).

Pension and Other Postretirement Benefit Plans

Williams has noncontributory defined benefit pension plans (Williams Pension Plan, Williams Inactive Employees Pension Plan, and The Williams Companies Retirement Restoration Plan) that provide pension benefits for its eligible employees hired prior to January 1, 2019. We received pension credits from Williams of $0.2 million in 2023, and pension charges of $0.7 million in 2022 and $0.8 million in 2021.

Williams provides subsidized retiree medical benefits to a closed group of participants as well as retiree life insurance to eligible participants. During 2023, 2022, and 2021, we received credits from Williams related to retiree medical and life insurance benefits of $0.2 million, $1.2 million and $1.6 million, respectively. These credits were recorded as regulatory liabilities.

We have been allowed by rate case settlements to collect or refund in future rates any differences between the actuarially determined costs and amounts currently being recovered in rates related to other postretirement benefits. Any differences between the annual actuarially determined cost and amounts currently being recovered in rates are recorded as regulatory assets or liabilities and collected or refunded through future rate adjustments. The amounts of other postretirement benefits costs deferred as regulatory liabilities at December 31, 2023 and 2022 are $42.4 million and $42.2 million, respectively.

Defined Contribution Plan

Williams maintains a defined contribution plan for substantially all of its employees. Williams charged us compensation expense of $3.0 million in 2023, $2.8 million in 2022 and $2.7 million in 2021 for Williams’ company contributions to this plan.

Employee Stock-Based Compensation Plan Information

The Williams Companies, Inc. 2007 Incentive Plan (the Plan), as subsequently amended and restated, provides for Williams’ common stock-based awards to both employees and non-management directors. The Plan permits the granting of various types of awards including, but not limited to, restricted stock units and stock options. Awards may be granted for no consideration other than prior and future services or based on certain financial performance targets achieved.

Williams currently bills us directly for compensation expense related to stock-based compensation awards based on the fair value of the awards. We are also billed for our proportionate share of Williams’ and other affiliates’ stock-based compensation expense through various allocation processes.

Total stock-based compensation expense for the years ended December 31, 2023, 2022 and 2021 was $1.5 million, $1.3 million and $1.2 million, respectively, excluding amounts allocated from Williams.

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Financial Instruments (Notes)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Financial Instruments

Fair Value Measurements

Fair Value Methods

The following methods and assumptions were used to estimate the fair value of each class of financial instruments for which it is practicable to estimate that value:

Short-term financial assets: The carrying values of short-term financial assets that have variable interest rates (advances to affiliate), accounts receivable and accounts payable approximate fair value because of the short-term nature of these instruments.

Long-term debt: The disclosed fair value of our long-term debt, which we consider as a level 2 measurement, is determined by a market approach using broker quoted indicative period-end bond prices. The quoted prices are based on observable transactions in less active markets for our debt or similar instruments. The carrying amount and estimated fair value of our long-term debt, including current maturities, were $581.2 million and $581.1 million, respectively, at December 31, 2023, and $580.1 million and $560.2 million, respectively, at December 31, 2022.

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Transactions with Major Customers and Affiliates (Notes)

12 Months Ended

Dec. 31, 2023

Transactions with Major Customers and Affiliates [Abstract]

Transactions with Major Customers and Affiliates

Major Customers

During the periods presented, more than 10 percent of our operating revenues were generated from each of the following customers:

	Year Ended December 31,
	2023		2022		2021
	(Thousands)
Puget Sound Energy, Inc.	$	126,206	$	130,705	$	131,462
Cascade Natural Gas Corporation	47,046		48,664		49,078
Northwest Natural Gas Company	46,637		48,921		48,901

Our major customers are located in the Pacific Northwest. As a general policy, collateral is not required for receivables, but customers’ financial condition and credit worthiness are regularly evaluated and historical collection losses have been minimal.

Affiliates

We are a participant in Williams’ cash management program. At December 31, 2023 and 2022, our advances to Williams totaled approximately $157.8 million and $310.6 million, respectively. These advances are represented by demand notes and are classified as Receivables - Advances to affiliate on the Balance Sheet. The interest rate on these intercompany demand notes is based upon the daily overnight investment rate paid on Williams’ excess cash at the end of each month, which was approximately 5.2 percent at December 31, 2023. The interest income from these advances was $8.3 million and $4.9 million for the years ended December 31, 2023 and 2022, respectively. The interest income from these advances was minimal for the year ended December 31, 2021. Such interest income is included in Other (Income) and Other Expenses - Miscellaneous other (income) expense, net on the Statement of Net Income.

We have no employees. Services necessary to operate our business are provided to us by Williams and certain affiliates of Williams. We reimburse Williams and its affiliates for all direct and indirect expenses incurred or payments made (including salary, bonus, incentive compensation, and benefits) in connection with these services. Employees of Williams also provide general, administrative and management services to us, and we are charged for certain administrative expenses incurred by

Williams. These charges are either directly identifiable or allocated to our assets. Direct charges are for goods and services provided by Williams at our request. Allocated charges are based on a three-factor formula, which considers revenues; property, plant, and equipment; and payroll. In management’s estimation, the allocation methodologies used are reasonable and result in a reasonable allocation to us of our costs of doing business incurred by Williams. We have recorded $86.0 million, $87.7 million, and $85.2 million for the years ended December 31, 2023, 2022, and 2021, respectively, for these service expenses, which are primarily included in Operation and maintenance and General and administrative expenses on the Statement of Net Income.

During January 2024, we declared and paid a cash distribution of $33.0 million to our parent.

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Asset Retirement Obligations (Notes)

12 Months Ended

Dec. 31, 2023

Asset Retirement Obligation Disclosure [Abstract]

Asset Retirement Obligations

Asset Retirement Obligations

Our accrued asset retirement obligations relate to our gas storage and transmission facilities. At the end of the useful life of our facilities, we are legally obligated to remove or plug and abandon certain transmission facilities including underground pipelines, major river spans, compressor stations and meter station facilities. These obligations also include restoration of the property sites after removal of the facilities from above and below the ground. Our overall asset retirement obligation changed as follows:

	Year Ended December 31,
	2023		2022
	(Thousands)
Beginning balance	$	129,306	$	122,650
Accretion	7,017		6,656
Changes in estimates of existing obligations (1)	(60)		—
Ending balance	$	136,263	$	129,306

______________________

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Regulatory Assets and Liabilities (Notes)

12 Months Ended

Dec. 31, 2023

Regulatory Assets and Liabilities Disclosure [Abstract]

Regulatory Assets and Liabilities

Regulatory Assets and Liabilities

The regulatory assets and regulatory liabilities resulting from our application of the provisions of Topic 980 included on the accompanying Balance Sheet are as follows:

	December 31,
	2023		2022
	(Thousands)
Current regulatory assets:
Fuel recovery	$	19	$	11,871
Levelized depreciation	2,035		1,694
Total current regulatory assets	2,054		13,565
Long-term regulatory assets:
Levelized depreciation	9,519		11,601
Grossed-up deferred taxes on equity funds used during construction	3,969		4,350
Washington State Carbon and Greenhouse Gas Tax	22,308		—
Total long-term regulatory assets	35,796		15,951
Total regulatory assets	$	37,850	$	29,516
Current regulatory liabilities:
Customer tax refund	$	—	$	125,506
Deferred federal taxes - liability	18,643		18,643
Deferred state taxes - liability	1,094		1,094
Fuel recovery	1,637		—
Total current regulatory liabilities	21,374		145,243
Long-term regulatory liabilities:
Deferred federal taxes - liability	169,240		187,883
Postretirement benefits	42,415		42,207
Asset retirement obligations, net	30,685		30,590
Deferred state taxes - liability	9,932		11,026
Total long-term regulatory liabilities	252,272		271,706
Total regulatory liabilities	$	273,646	$	416,949

The significant regulatory assets and liabilities include:

Fuel Recovery: This amount represents the value of the cumulative volumetric difference between the gas retained from our customers and the gas consumed in operations. These amounts are not included in the rate base but assets and liabilities are expected to be recovered or refunded, respectively, by changing the fuel reimbursement rate in subsequent annual fuel filings.

Levelized Depreciation: Levelized depreciation allows contract revenue streams to remain constant over the primary contract terms by recognizing lower than book depreciation in the early years and higher than book depreciation in later years. The depreciation component of the levelized incremental rates will equal the accumulated book depreciation by the end of the primary contract terms. The difference between levelized depreciation and straight-line book depreciation is recorded as a FERC approved regulatory asset or liability and is eliminated over the levelization period.

Grossed-Up Deferred Taxes on Equity Funds Used During Construction: The regulatory asset balance was established to offset the deferred tax for the equity component of the allowance for funds used during the construction of long-lived assets. All amounts were generated during the period that we were a taxable entity. Taxes on capitalized funds used during construction and the offsetting deferred income taxes are included in the rate base and are recovered over the depreciable lives of the long-lived assets to which they relate.

Customer Tax Refund: In our 2017 Settlement, which became effective January 1, 2018, we agreed with our customers that if federal income tax rates decreased due to subsequent legislation, such as the Tax Cuts and Jobs Act of 2017 (Tax Reform), we would record a regulatory liability. As a result of Tax Reform and as stipulated in the Docket No. RP22-1155 rate case settlement, the accrued regulatory liability, including interest, was paid to customers in January 2023.

Deferred Federal Taxes - Liability: This regulatory liability balance was established as a result of a decrease to rate base deferred taxes due to a decrease to the effective federal income tax rate. The timing of the refund of the regulatory liability to rate payers is stated in the Docket No. RP22-1155 rate case settlement.

Postretirement Benefits: We seek to recover the actuarially determined cost of postretirement benefits through rates that are set through periodic general rate filings. Any differences between the annual actuarially determined cost and amounts currently being recovered in rates are recorded as regulatory assets or liabilities and collected or refunded through future rate adjustments. These amounts are not included in the rate base, and we are not currently recovering postretirement benefit costs in our rates (see Note 7 – Benefit Plans).

ARO, net: This regulatory liability balance reflects the amount that we have recovered in our rates related to our future retirement costs offset by depreciation of the ARO asset and changes in the ARO liability due to the passage of time. AROs are expected to be fully recovered through the net negative salvage component of depreciation included in our rates (see Note 10 – Asset Retirement Obligations).

Deferred State Taxes - Liability: This regulatory liability balance, following the August 10, 2018 merger of Williams with Williams Partners L.P., reflects a decrease to rate base deferred taxes due to a decrease to the estimated effective state income tax rates. The timing of the refund of the regulatory liability to rate payers is stated in the Docket No. RP22-1155 rate case settlement.

Washington State Carbon and Greenhouse Tax: This amount represents the cost of emission allowances and the associated accumulated interest as a result of the passage of the state of Washington Climate Commitment Act that took effect January 1, 2023. Our Settlement allows us to recover the costs of purchasing allowances under the program in our next rate case.

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Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Use of Estimates

Use of Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates.

Significant estimates and assumptions include:

•Litigation-related contingencies;

•Environmental remediation obligations;

•Impairment assessments of long-lived assets;

•Depreciation;

•Asset retirement obligations; and

•Measurement of regulatory assets and liabilities.

These estimates are discussed further throughout these notes.

Regulatory Accounting

Regulatory Accounting

We are regulated by the Federal Energy Regulatory Commission (FERC). Accounting Standards Codification (ASC) Topic 980, “Regulated Operations,” (Topic 980), provides that certain costs that would otherwise be charged to expense should be deferred as regulatory assets, based on the expected recovery from customers in future rates. Likewise, certain actual or anticipated credits that would otherwise reduce expense should be deferred as regulatory liabilities, based on the expected return to customers in future rates. Management's expected recovery of deferred costs and return of deferred credits generally results from specific decisions by regulators granting such ratemaking treatment. We record certain incurred costs and obligations as regulatory assets or liabilities if, based on regulatory orders or other available evidence, it is probable that the costs or obligations will be included in amounts allowable for recovery or refunded in future rates. Accounting for businesses that are regulated and apply the provisions of Topic 980 can differ from the accounting requirements for non-regulated businesses. Transactions that are recorded differently as a result of regulatory accounting requirements include the capitalization of an equity return component on regulated capital projects, capitalization of other project costs, retirements of general plant assets, levelized cost of service, negative salvage, asset retirement obligations (ARO), employee-related benefits, environmental costs, and other costs and taxes included in, or expected to be included in, future rates. As a rate-regulated entity, our management has determined that it is appropriate to apply the accounting prescribed by Topic 980, and, accordingly, the

accompanying financial statements include the effects of the types of transactions described above that result from regulatory accounting requirements.

Revenue Recognition

Revenue Recognition

Our customers are comprised of public utilities, municipalities, direct industrial users, electric power generators, and natural gas marketers and producers.

Service revenue contracts from our gas pipeline business contain a series of distinct services, with the majority of our contracts having a single performance obligation that is satisfied over time as the customer simultaneously receives and consumes the benefits provided by our performance.

Certain customers reimburse us for costs we incur associated with construction of property, plant, and equipment utilized in our operations. As a rate-regulated entity applying Topic 980, we follow FERC guidelines with respect to reimbursement of construction costs. FERC tariffs only allow for cost reimbursement and are non-negotiable in nature; thus, in our judgment, the construction activities do not represent an ongoing major and central operation of our gas pipeline business and are not within the scope of ASC Topic 606, “Revenues from Contracts with Customers.” Accordingly, cost reimbursements are treated as a reduction to the cost of the constructed asset.

Operating Revenues

We are subject to regulation by certain state and federal authorities, including the FERC, with revenue derived from both firm and interruptible transportation and storage contracts. Firm transportation and storage agreements provide for a fixed reservation charge based on the pipeline or storage capacity reserved, and a commodity charge based on the volume of natural gas delivered/stored, each at rates specified in our FERC tariffs or as negotiated with our customers, with contract terms that are generally long-term in nature. Most of our long-term contracts contain an evergreen provision, which allows the contracts to be extended for periods primarily up to one year in length an indefinite number of times following the specified contract term and until terminated generally by either us or the customer, but in certain cases unilaterally by the customer, with advance notice of termination ranging from one to five years. Interruptible transportation and storage agreements provide for a volumetric charge based on actual commodity transportation or storage utilized in the period in which those services are provided, and the contracts are generally limited to one-month periods or less. Our performance obligations include the following:

•Firm transportation or storage under firm transportation and storage contracts—an integrated package of services typically constituting a single performance obligation, which includes standing ready to provide such services and receiving, transporting or storing (as applicable), and redelivering commodities;

•Interruptible transportation and storage under interruptible transportation and storage contracts—an integrated package of services typically constituting a single performance obligation once scheduled, which includes receiving, transporting or storing (as applicable), and redelivering commodities.

In situations where, in our judgment, we consider the integrated package of services as a single performance obligation, which represents a majority of our contracts with customers, we do not consider there to be multiple performance obligations because the nature of the overall promise in the contract is to stand ready (with regard to firm transportation and storage contracts), receive, transport or store, and redeliver natural gas to the customer; therefore, revenue is recognized over time upon satisfaction of our daily stand ready performance obligation.

We recognize revenues for reservation charges over the performance obligation period, which is the contract term, regardless of the volume of natural gas that is transported or stored. Revenues for commodity charges from both firm and interruptible transportation services and storage services are recognized when natural gas is delivered at the agreed upon point or when natural gas is injected or withdrawn from the storage facility because they specifically relate to our efforts to provide these distinct services. Generally, reservation charges and commodity charges are recognized as revenue in the same period they are invoiced to our customers. As a result of the ratemaking process, certain amounts collected by us may be subject to refunds upon the issuance of final orders by the FERC in pending rate proceedings. We use judgment to record estimates of rate refund liabilities considering our and other third-party regulatory proceedings, advice of counsel, and other risks. At December 31, 2023 and 2022, we had no such rate refund liabilities.

In the course of providing transportation services to customers, we may receive different quantities of natural gas from customers than the quantities delivered on behalf of those customers or consumed in fuel to operate our system. The resulting

customer imbalances are typically settled through the receipt or delivery of gas in the future based on the timelines outlined in Northwest’s tariff, whereas the over/under recovery of fuel is cleared up through Northwest’s semi-annual fuel tracker. Customer imbalances to be repaid or recovered in-kind are recorded as Exchange gas receivables or Exchange gas payables in our Balance Sheet. The under recovery of fuel is recorded as a Regulatory Asset and the over recovery is recorded as a Regulatory Liability. These imbalances are valued at published spot rates.

Contract Assets

Our contract assets consist of discounts provided to customers in the beginning of the contract term that are recognized on a straight-line basis over the entire contract term resulting in revenue recognition occurring prior to actual billings. Contract assets are included within Other on our Balance Sheet.

Contract Liabilities

Our contract liabilities consist of a fixed rate facility charge billed to customers that declines annually as specified per the tariff. These liabilities are classified as current or non-current according to when such amounts are expected to be recognized. Current and non-current liabilities are included within Accrued Liabilities and Other Long-Term Liabilities, respectively, on our Balance Sheet.

Leases

Leases

We are a lessee through noncancellable lease agreements for property and equipment consisting primarily of buildings, land, vehicles, and equipment used in both our operations and administrative functions. We recognize a lease liability with an offsetting right-of-use asset in our Balance Sheet for operating leases based on the present value of the future lease payments. We have elected to combine lease and nonlease components for all classes of leased assets in our calculation of the lease liability and the offsetting right-of-use asset.

Our lease agreements require both fixed and variable periodic payments, with initial terms typically ranging from one year to 30 years. Payment provisions in certain of our lease agreements contain escalation factors which may be based on stated rates or a change in a published index at a future time. The amount by which a lease escalates based on the change in a published index, which is not known at lease commencement, is considered a variable payment and is not included in the present value of the future lease payments, which only includes those that are stated or can be calculated based on the lease agreement at lease commencement. In addition to the noncancellable periods, many of our lease agreements provide for one or more extensions of the lease agreement for periods ranging from one year in length to an indefinite number of times following the specified contract term. Other lease agreements provide for extension terms that allow us to utilize the identified leased asset for an indefinite period of time so long as the asset continues to be utilized in our operations. In consideration of these renewal features, we assess the term of the lease agreements, which includes using judgment in the determination of which renewal periods and termination provisions, when at our sole election, will be reasonably certain of being exercised. Periods after the initial term or extension terms that allow for either party to the lease to cancel the lease are not considered in the assessment of the lease term. Additionally, we have elected to exclude leases with an original term of one year or less, including renewal periods, from the calculation of the lease liability and the offsetting right-of-use asset.

We use judgment in determining the discount rate upon which the present value of the future lease payments is determined. This rate is based on a collateralized interest rate corresponding to the term of the lease agreement using company, industry, and market information available.

Environmental Matters

Environmental Matters

We are subject to federal, state, and local environmental laws and regulations. Environmental expenditures are expensed or capitalized depending on their economic benefit and potential for rate recovery. We believe that expenditures required to meet applicable environmental laws and regulations are prudently incurred in the ordinary course of business and such expenditures would be permitted to be recovered through rates.

Greenhouse Gas Emission Allowances

In accordance with the Climate Commitment Act of the state of Washington, which established a market-based cap-and-invest program, we are required to obtain emission allowances for the carbon emissions from nine of our thirteen compressor stations within the state of Washington whose annual carbon emissions exceed 25,000 metric tons of carbon dioxide equivalent. We record the purchased emission allowances at cost and the associated accumulated interest to a regulatory asset. The difference between the allowances held and the allowances required based on actual emissions for the period are measured using an estimate based on our most recent cost of allowances and accrued to a current liability and to a regulatory asset. Our Settlement allows us to recover the costs of purchasing allowances under the program in our next rate case.

Property, Plant, and Equipment

Property, Plant, and Equipment

Property, plant and equipment, consisting principally of natural gas transmission facilities, is recorded at cost. The FERC identifies installation, construction and replacement costs that are to be capitalized and included in our asset base for recovery in rates. Routine maintenance, repairs, and renewal costs are charged to income as incurred. Gains or losses from the ordinary sale or retirement of property, plant and equipment are charged or credited to accumulated depreciation; certain other gains or losses are recorded in operating income.

We provide for depreciation under the composite (group) method at straight-line FERC prescribed rates that are applied to the cost of the group for transmission and storage facilities. Under this method, assets with similar lives and characteristics are grouped and depreciated as one asset. Included in our depreciation rates is a negative salvage component (net cost of removal) that we currently collect in rates. Our depreciation rates are subject to change each time we file a general rate case with the FERC.

The following table presents Total property, plant and equipment, net as presented on the Balance Sheet:

	Depreciation Rate	December 31,
		2023		2022
		(Thousands)
Transmission facilities	2.70%  -  10.20%	$	3,569,545	$	3,490,141
Storage facilities	1.60%  -  2.76%	155,433		142,326
Construction in progress	Not applicable	84,945		44,702
Other	0% - 33.33%	164,977		159,085
Property, plant and equipment		3,974,900		3,836,254
Less-Accumulated depreciation and amortization		2,026,007		1,941,806
Total property, plant and equipment, net		$	1,948,893	$	1,894,448

We record a liability and increase the basis in the underlying asset for the present value of each expected future ARO at the time the liability is initially incurred, typically when the asset is acquired or constructed. Measurement of ARO includes, as a component of future expected costs, an estimate of the price that a third party would demand, and could expect to receive, for bearing the uncertainties inherent in the obligations, sometimes referred to as market-risk premium. We measure changes in the liability due to passage of time by applying an interest method of allocation. This amount is recognized as an increase in the carrying amount of the liability and is offset by a regulatory asset. The gross regulatory asset balances associated with ARO as of December 31, 2023 and 2022 were $116.2 million and $109.0 million, respectively. The regulatory asset is expected to be fully recovered through the negative salvage component of depreciation included in our rates; as such, that amount of the negative salvage component of accumulated depreciation has been reclassified and netted against the amount of the ARO regulatory asset to result in a regulatory liability of $30.7 million and $30.6 million at December 31, 2023 and 2022, respectively.

Allowance for Funds Used During Construction

Allowance for Funds Used During Construction

Allowance for funds used during construction (AFUDC) represents the estimated cost of borrowed and equity funds applicable to utility plant in process of construction and is included as a cost of property, plant and equipment because it

constitutes an actual cost of construction under established regulatory practices. The FERC has prescribed a formula to be used in computing separate allowances for borrowed and equity AFUDC. The allowance for borrowed funds used during construction was $0.7 million for 2023, $0.7 million for 2022, and $0.2 million for 2021. The allowance for equity funds was $3.1 million, $2.3 million, and $1.4 million for 2023, 2022, and 2021, respectively.

Income Taxes

Income Taxes

We are a natural gas company organized as a pass-through entity and our taxable income or loss is consolidated on the federal income tax return of our parent, Williams. We generally are treated as a pass-through entity for state and local income tax purposes, and those taxes are generally borne on a consolidated basis by Williams. Net income for financial statement purposes may differ significantly from taxable income of Williams as a result of differences between the tax basis and financial reporting basis of assets and liabilities.

Accounts Receivable and Allowance for Doubtful Receivables

Accounts Receivable

Accounts receivable are carried on a gross basis less an allowance for doubtful accounts. We estimate the allowance for doubtful accounts, considering current expected credit losses using a forward-looking “expected loss” model, the financial condition of our customers, and the age of past due accounts. The majority of our trade receivable balances are due within 30 days. We monitor the credit quality of our counterparties through review of collection trends, credit ratings, and other analyses, such as bankruptcy monitoring, if applicable. Financial assets are evaluated as one pool. Changes in counterparty risk factors could lead to reassessment of the composition of our financial assets as one pool. We calculate our allowance for credit losses incorporating an aging method. In estimating our expected credit losses, we utilized historical loss rates over many years. Our expected credit loss estimate considered both internal and external forward-looking commodity price expectations, as well as counterparty credit ratings, and factors impacting their near-term liquidity.

We do not offer extended payment terms and typically receive payment within one month. We consider receivables past due if full payment is not received by the contractual due date. Past due accounts are generally written off against the allowance for doubtful accounts only after all collection attempts have been exhausted. We do not have a material amount of significantly aged receivables at December 31, 2023 and 2022.

Materials and Supplies Inventory

Materials and Supplies Inventory

All materials and supplies inventory is stated at average cost. We perform an annual review of materials and supplies inventories, including a quarterly analysis of parts that may no longer be useful due to planned replacements of compressor engines and other components on our system. Based on this assessment, we record a reserve for the value of the inventory which can no longer be used for maintenance and repairs on our pipeline. The reserve for inventory was $1.0 million at December 31, 2023, and there was a minimal reserve at December 31, 2022.

Contingent Liabilities

Contingent Liabilities

We record liabilities for estimated loss contingencies, including environmental matters, when we assess that a loss is probable and the amount of the loss can be reasonably estimated. These liabilities are calculated based upon our assumptions and estimates with respect to the likelihood or amount of loss and upon advice of legal counsel, engineers, or other third-parties regarding the probable outcomes of the matters. These calculations are made without consideration of any potential recovery from third-parties. We recognize insurance recoveries or reimbursements from others when realizable. Revisions to these liabilities are generally reflected in income when new or different facts or information become known or circumstances change that affect the previous assumptions or estimates.

Pension and Other Postretirement Benefits

Pension and Other Postretirement Benefits

We do not have employees. Certain of the costs charged to us by Williams associated with employees who directly support us include costs related to Williams’ pension and other postretirement benefit plans (see Note 7 – Benefit Plans). Although the underlying benefit plans of Williams are single-employer plans, we follow multiemployer plan accounting whereby the amount charged to us, and thus paid by us, is based on our share of net periodic benefit cost.

Cash Flows from Operating Activities

Cash Flows from Operating Activities

We use the indirect method to report cash flows from operating activities, which requires adjustments to net income to reconcile to net cash flows provided by operating activities.

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Financial Instruments (Policies)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Fair value of financial instruments

Fair Value Methods

The following methods and assumptions were used to estimate the fair value of each class of financial instruments for which it is practicable to estimate that value:

Short-term financial assets: The carrying values of short-term financial assets that have variable interest rates (advances to affiliate), accounts receivable and accounts payable approximate fair value because of the short-term nature of these instruments.

Long-term debt: The disclosed fair value of our long-term debt, which we consider as a level 2 measurement, is determined by a market approach using broker quoted indicative period-end bond prices. The quoted prices are based on observable transactions in less active markets for our debt or similar instruments. The carrying amount and estimated fair value of our long-term debt, including current maturities, were $581.2 million and $581.1 million, respectively, at December 31, 2023, and $580.1 million and $560.2 million, respectively, at December 31, 2022.

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Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Total property, plant and equipment, net

The following table presents Total property, plant and equipment, net as presented on the Balance Sheet:

	Depreciation Rate	December 31,
		2023		2022
		(Thousands)
Transmission facilities	2.70%  -  10.20%	$	3,569,545	$	3,490,141
Storage facilities	1.60%  -  2.76%	155,433		142,326
Construction in progress	Not applicable	84,945		44,702
Other	0% - 33.33%	164,977		159,085
Property, plant and equipment		3,974,900		3,836,254
Less-Accumulated depreciation and amortization		2,026,007		1,941,806
Total property, plant and equipment, net		$	1,948,893	$	1,894,448

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Revenue Recognition (Tables)

12 Months Ended

Dec. 31, 2023

Revenue Recognition [Abstract]

Contract with Customer, Asset and Liability [Table Text Block]

Contract Assets

The following table presents a reconciliation of our contract assets:

	Year Ended December 31,
	2023		2022
	(Thousands)
Balance at beginning of period	$	12,490	$	7,943
Revenue recognized in excess of amounts invoiced	4,316		4,547
Balance at end of period	$	16,806	$	12,490

Contract Liabilities

The following table presents a reconciliation of our contract liabilities:

	Year Ended December 31,
	2023		2022
	(Thousands)
Balance at beginning of period	$	2,643	$	3,672
Recognized in revenue	(1,175)		(1,029)
Balance at end of period	$	1,468	$	2,643

Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block]

The following table presents the amount of the contract liabilities balance expected to be recognized as revenue when performance obligations are satisfied and the transaction price allocated to the remaining performance obligations under certain contracts as of December 31, 2023.

	Contract Liabilities		Remaining Performance Obligations
	(Thousands)
2024 (one year)	$	1,178	$	386,252
2025 (one year)	290		369,844
2026 (one year)	—		354,605
2027 (one year)	—		351,285
2028 (one year)	—		345,753
Thereafter	—		2,228,679
Total	$	1,468	$	4,036,418

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Leases Leases (Tables)

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Lease, Cost [Table Text Block]

	Year Ended December 31,
	2023		2022		2021
	(Thousands)
Lease Cost:
Operating lease cost	$	1,205	$	1,226		$	1,334
Variable lease cost	588		578			681
Total lease cost	$	1,793	$	1,804		$	2,015
Cash paid for operating lease liabilities	$	954	$	950		$	2,395
			December 31,
			2023			2022
			(Thousands)
Other Information:
Right-of-use assets			$	8,725		$	9,621
Operating lease liabilities:
Current (included in Accrued liabilities - Other on our Balance Sheet)			$	701		$	681
Lease liability			$	7,193		$	7,857
Weighted-average remaining lease term - operating leases (years)			15			16
Weighted-average discount rate - operating leases			4.18%			4.12%

Lessee, Operating Lease, Liability, Maturity [Table Text Block]

As of December 31, 2023, the following table represents our operating lease maturities, including renewal provisions that we have assessed as being reasonably certain of exercise, for each of the years ended December 31:

	(Thousands)
2024	$	954
2025	971
2026	973
2027	987
2028	961
Thereafter	6,651
Total future lease payments	11,497
Less amount representing interest	3,603
Total obligations under operating leases	$	7,894

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Debt Disclosure (Tables)

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Long-term debt

	December 31,
	2023		2022
	(Thousands)
7.125% Debentures due 2025	$	85,000	$	85,000
4.0% Notes due 2027	500,000		500,000
Unamortized debt issuance costs	(1,954)		(2,517)
Unamortized debt discount	(1,868)		(2,400)
Total long-term debt	$	581,178	$	580,083

Maturities of long-term debt

The following table reflects future maturities of long-term (at face value) debt for the next five years (in thousands):

2025	$	85,000
2027	$	500,000

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Transactions with Major Customers and Affiliates (Tables)

12 Months Ended

Dec. 31, 2023

Transactions with Major Customers and Affiliates [Abstract]

Schedule of revenue by major customers

During the periods presented, more than 10 percent of our operating revenues were generated from each of the following customers:

	Year Ended December 31,
	2023		2022		2021
	(Thousands)
Puget Sound Energy, Inc.	$	126,206	$	130,705	$	131,462
Cascade Natural Gas Corporation	47,046		48,664		49,078
Northwest Natural Gas Company	46,637		48,921		48,901

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Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2023

Asset Retirement Obligation Disclosure [Abstract]

Schedule of change in asset retirement obligation

ur overall asset retirement obligation changed as follows:

	Year Ended December 31,
	2023		2022
	(Thousands)
Beginning balance	$	129,306	$	122,650
Accretion	7,017		6,656
Changes in estimates of existing obligations (1)	(60)		—
Ending balance	$	136,263	$	129,306

______________________

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Regulatory Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2023

Regulatory Assets and Liabilities Disclosure [Abstract]

Schedule of Regulatory Assets and Liabilities [Table Text Block]

	December 31,
	2023		2022
	(Thousands)
Current regulatory assets:
Fuel recovery	$	19	$	11,871
Levelized depreciation	2,035		1,694
Total current regulatory assets	2,054		13,565
Long-term regulatory assets:
Levelized depreciation	9,519		11,601
Grossed-up deferred taxes on equity funds used during construction	3,969		4,350
Washington State Carbon and Greenhouse Gas Tax	22,308		—
Total long-term regulatory assets	35,796		15,951
Total regulatory assets	$	37,850	$	29,516
Current regulatory liabilities:
Customer tax refund	$	—	$	125,506
Deferred federal taxes - liability	18,643		18,643
Deferred state taxes - liability	1,094		1,094
Fuel recovery	1,637		—
Total current regulatory liabilities	21,374		145,243
Long-term regulatory liabilities:
Deferred federal taxes - liability	169,240		187,883
Postretirement benefits	42,415		42,207
Asset retirement obligations, net	30,685		30,590
Deferred state taxes - liability	9,932		11,026
Total long-term regulatory liabilities	252,272		271,706
Total regulatory liabilities	$	273,646	$	416,949

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Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 3,974,900	$ 3,836,254
Less-Accumulated depreciation and amortization	2,026,007	1,941,806
Property, Plant and Equipment, Net	1,948,893	1,894,448
Regulatory Assets	37,850	29,516
Regulatory Liabilities	273,646	416,949
Capitalized Interest Costs, Including Allowance for Funds Used During Construction [Abstract]
Allowance for funds used during construction, debt	700	700	$ 200
Allowance for funds used during construction, equity	3,100	2,300	1,400
Interest Payments [Abstract]
Cash payments for interest, net of interest capitalized	26,100	26,100	$ 26,100
Other Regulatory Assets (Liabilities) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Regulatory Liabilities	30,700	30,600
Asset Retirement Obligation
Public Utility, Property, Plant and Equipment [Line Items]
Regulatory Assets	116,200	109,000
Transmission facilities
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	3,569,545	3,490,141
Storage facilities
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	155,433	142,326
Construction in progress
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	84,945	44,702
Other
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 164,977	$ 159,085
Minimum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract	1 year
Minimum [Member] | Transmission facilities
Public Utility, Property, Plant and Equipment [Line Items]
Depreciaton rates	2.70%
Minimum [Member] | Storage facilities
Public Utility, Property, Plant and Equipment [Line Items]
Depreciaton rates	1.60%
Minimum [Member] | Other
Public Utility, Property, Plant and Equipment [Line Items]
Depreciaton rates	0.00%
Maximum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract	30 years
Maximum [Member] | Transmission facilities
Public Utility, Property, Plant and Equipment [Line Items]
Depreciaton rates	10.20%
Maximum [Member] | Storage facilities
Public Utility, Property, Plant and Equipment [Line Items]
Depreciaton rates	2.76%
Maximum [Member] | Other
Public Utility, Property, Plant and Equipment [Line Items]
Depreciaton rates	33.33%

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Contract Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Revenue Recognition [Abstract]
Contract with Customer, Asset, Net - Beginning of Period	$ 12,490	$ 7,943
Revenue recognized in excess of amounts invoiced	4,316	4,547
Contract with Customer, Asset, Net - End of Period	$ 16,806	$ 12,490

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Revenue from Contract Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Contract With Customer, Liability [Line Items]
Contract with Customer, Liability - Balance at beginning of period	$ 2,643	$ 3,672
Recognized in Revenue	(1,175)	(1,029)
Contract with Customer, Liability - Balance at end of Period	1,468	$ 2,643
Revenue, Remaining Performance Obligation, Amount	$ 4,036,418

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Contract Liabilities Performance Obligation (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 4,036,418
Contract with Customer, Liability - Beginning of Period	1,468	$ 2,643	$ 3,672
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	386,252
Contract with Customer, Liability - Beginning of Period	$ 1,178
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01 | Performance Obligations Related To Contract Liabilities [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01 | Remaining Performance Obligations [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 369,844
Contract with Customer, Liability - Beginning of Period	$ 290
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01 | Performance Obligations Related To Contract Liabilities [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01 | Remaining Performance Obligations [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 354,605
Contract with Customer, Liability - Beginning of Period	$ 0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01 | Performance Obligations Related To Contract Liabilities [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01 | Remaining Performance Obligations [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 351,285
Contract with Customer, Liability - Beginning of Period	$ 0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01 | Performance Obligations Related To Contract Liabilities [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01 | Remaining Performance Obligations [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 345,753
Contract with Customer, Liability - Beginning of Period	$ 0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01 | Performance Obligations Related To Contract Liabilities [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01 | Remaining Performance Obligations [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 2,228,679
Contract with Customer, Liability - Beginning of Period	$ 0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01 | Performance Obligations Related To Contract Liabilities [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01 | Remaining Performance Obligations [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period

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Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Operating lease cost	$ 1,205	$ 1,226	$ 1,334
Variable lease cost	588	578	681
Total lease cost	1,793	1,804	2,015
Cash paid for operating lease liabilities	954	950	$ 2,395
Right-of-use assets	8,725	9,621
Current (included in Accrued liabilities - Other on our Balance Sheet)	$ 701	$ 681
Current (included in Accrued liabilities - Other on our Balance Sheet)	Other	Other
Lease liability	$ 7,193	$ 7,857
Weighted-average remaining lease term - operating leases (years)	15 years	16 years
Weighted-average discount rate - operating leases	4.18%	4.12%
2024	$ 954
2025	971
2026	973
2027	987
2028	961
Thereafter	6,651
Total future lease payments	11,497
Less amount representing interest	3,603
Total obligations under operating leases	$ 7,894

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Regulated Operations (Details)	Nov. 15, 2022 $ / dekatherm
Regulated Operations [Abstract]
Demand Rate	0.37250
Commodity Rate	0.00935

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Contingent Liabilities and Commitments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Site Contingency [Line Items]
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration]	Other, Other	Other, Other
Environmental Loss Contingency, Current, Statement of Financial Position [Extensible Enumeration]	Other	Other
Environmental Loss Contingency, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other	Other
Regulatory assets	$ 2,054	$ 13,565
Other	10,588	4,011
Environmental assessment and remediation
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies, Total	1,000	1,000
Accrued environmental assessment and remediation costs, current	200	100
Accrued environmental assessment and remediation costs, noncurrent	800	$ 900
Washington State Climate Commitment Act [Member]
Site Contingency [Line Items]
Regulatory assets	22,300
Other	3,700
Interest Income, affiliate	$ 600

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Debt and Financing Arrangements (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022	Oct. 08, 2021	Jul. 13, 2018
Debt Instrument [Line Items]
Long-term Debt	$ 581,178,000	$ 580,083,000
Issuance of debt	1,954,000	2,517,000
Debt Instrument, Unamortized Discount	1,868,000	2,400,000
Long-term Debt, Fiscal Year Maturity [Abstract]
2025	85,000,000
2027	500,000,000
7.125 percent unsecured debentures due 2025 [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 85,000,000	85,000,000
Debt Instrument, Interest Rate, Stated Percentage	7.125%
4.0% unsecured debentures due 2027 [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 500,000,000	$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.00%
Asset Pledged as Collateral [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 0
Line of Credit [Member]
Credit Facility and Commercial Paper [Line Items]
Credit Facility Capacity			$ 500,000,000
Williams Companies Inc [Member]
Credit Facility and Commercial Paper [Line Items]
Commercial Paper Outstanding	725,000,000
Williams Companies Inc [Member] | Commercial Paper Program
Credit Facility and Commercial Paper [Line Items]
Credit Facility Capacity			3,500,000,000
Williams Companies Inc [Member] | Swing Line Loan
Credit Facility and Commercial Paper [Line Items]
Credit Facility Capacity			200,000,000
Williams Companies Inc [Member] | Line of Credit [Member]
Credit Facility and Commercial Paper [Line Items]
Credit Facility Capacity			3,750,000,000	$ 4,500,000,000
Additional Amount By Which Credit Facility Can Be Increased			$ 500,000,000
Loans Outstanding	0
Williams Companies Inc [Member] | Letter of Credit Commitments
Credit Facility and Commercial Paper [Line Items]
Credit Facility Capacity				$ 500,000,000
Letters of Credit Outstanding, Amount	$ 0
Transco [Member]
Credit Facility and Commercial Paper [Line Items]
Maximum Ratio Of Debt To Capitalization	65.00%
Northwest [Member]
Credit Facility and Commercial Paper [Line Items]
Maximum Ratio Of Debt To Capitalization	65.00%

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Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Pension cost	$ 200	$ (700)	$ (800)
Regulatory liabilities	252,272	271,706
Regulatory Liabilities	273,646	416,949
Defined contribution plan matching contributions expense	3,000	2,800	2,700
Salary and Wage, Excluding Cost of Good and Service Sold [Abstract]
Stock-based compensation expense	1,500	1,300	1,200
Retiree health care and life insurance benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory liabilities	200	1,200	$ 1,600
Other Postretirement Benefit Costs
Defined Benefit Plan Disclosure [Line Items]
Regulatory liabilities	$ 42,400	$ 42,200

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Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Fair Value	$ 581.2	$ 580.1
Estimate of fair value of long-term debt, including current maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Fair Value	$ 581.1	$ 560.2

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Transactions with Major Customers and Affiliates (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2024 USD ($)	Dec. 31, 2023 USD ($) employee	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Revenue, Major Customer [Line Items]
Operating revenues		$ 439,858	$ 447,335	$ 443,558
Related Party Transaction [Line Items]
Related party transaction, rate		5.20%
Entity number of employees | employee		0
Cash distributions to parent		$ 154,800	137,900	166,500
Related Party [Member]
Related Party Transaction [Line Items]
Advances to affiliate		157,776	310,641
Interest Income, affiliate		8,300		4,900
Related party transaction, expenses from transactions with related party		86,000	87,700	85,200
Williams Companies Inc [Member]
Related Party Transaction [Line Items]
Advances to affiliate		157,800	310,600
Subsequent Event [Member]
Related Party Transaction [Line Items]
Cash distributions to parent	$ 33,000
Puget Sound Energy, Inc.
Revenue, Major Customer [Line Items]
Operating revenues		126,206	130,705	131,462
Northwest Natural Gas Company
Revenue, Major Customer [Line Items]
Operating revenues		46,637	48,921	48,901
Cascade Natural Gas Corporation
Revenue, Major Customer [Line Items]
Operating revenues		$ 47,046	$ 48,664	$ 49,078

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Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	$ 129,306	$ 122,650
Accretion	7,017	6,656
Changes in estimates of existing obligations (1)	(60)	0
Ending balance	$ 136,263	$ 129,306

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Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Regulatory Assets [Line Items]
Regulatory assets	$ 2,054	$ 13,565
Regulatory assets, noncurrent	35,796	15,951
Total regulatory assets	37,850	29,516
Regulatory Liabilities [Line Items]
Regulatory liabilities	21,374	145,243
Regulatory liabilities	252,272	271,706
Total regulatory liabilities	273,646	416,949
Customer tax refund [Domain]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	125,506
Fuel recovery
Regulatory Liabilities [Line Items]
Regulatory liabilities	1,637	0
Postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities	42,415	42,207
Deferred federal taxes-liability
Regulatory Liabilities [Line Items]
Regulatory liabilities	18,643	18,643
Regulatory liabilities	169,240	187,883
Deferred state taxes - liability
Regulatory Liabilities [Line Items]
Regulatory liabilities	1,094	1,094
Regulatory liabilities	9,932	11,026
Asset retirement obligations, net [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	30,685	30,590
Fuel recovery
Regulatory Assets [Line Items]
Regulatory assets	19	11,871
Levelized depreciation
Regulatory Assets [Line Items]
Regulatory assets	2,035	1,694
Regulatory assets, noncurrent	9,519	11,601
Grossed-up deferred taxes on equity funds used during construction
Regulatory Assets [Line Items]
Regulatory assets, noncurrent	3,969	4,350
Washington State Carbon and Greenhouse Tax [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 22,308	$ 0