EXHIBIT 99.1

Westlake Chemical OpCo LP

Combined Financial Statements for the year ended December 31, 2014

1

Independent Auditor's Report

To the General Partner of Westlake Chemical OpCo LP:

We have audited the accompanying combined financial statements of Westlake Chemical OpCo LP, which comprise the combined balance sheetsas of December 31, 2014 and 2013, and the related combined statements of operations, of changes in equity and of cash flows for the three years in the period ended December 31, 2014.

Management's Responsibility for the Combined Financial Statements

Management is responsible for the preparation and fair presentation of the combined financial statements in accordance with accounting principles generally accepted in the United States of America; this includes the design, implementation, and maintenance of internal control relevant to the preparation and fair presentation of combined financial statements that are free from material misstatement, whether due to fraud or error.

Auditor's Responsibility

Our responsibility is to express an opinion on the combined financial statements based on our audits. We conducted our audits in accordance with auditing standards generally accepted in the United States of America and in accordance with the standards of the Public Company Accounting Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the combined financial statements are free from material misstatement.

An audit involves performing procedures to obtain audit evidence about the amounts and disclosures in the combined financial statements. The procedures selected depend on our judgment, including the assessment of the risks of material misstatement of the combinedfinancial statements, whether due to fraud or error. In making those risk assessments, we consider internal control relevant to the Company's preparation and fair presentation of the combined financial statements in order to design audit procedures that are appropriate in the circumstances, but not for the purpose of expressing an opinion on the effectiveness of the Company's internal control. Accordingly, we express no such opinion. An audit also includes evaluating the appropriateness of accounting policies used and the reasonableness of significant accounting estimates made by management, as well as evaluating the overall presentation of the combined financial statements. We believe that the audit evidence we have obtained is sufficient and appropriate to provide a basis for our audit opinion.

Opinion

In our opinion, the combined financial statements referred to above present fairly, in all material respects, the financial position of Westlake Chemical OpCo LP at December 31, 2014 and 2013, and the results of their operations and their cash flows for the three years in the period ended December 31, 2014 in accordance with accounting principles generally accepted in the United States of America.

/s/ PricewaterhouseCoopers LLP

Houston, Texas

February 25, 2015

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WESTLAKE CHEMICAL OPCO LP

COMBINED BALANCE SHEETS

	December 31, 2014		December 31, 2013
			Predecessor
	(in thousands of dollars)
ASSETS
Current assets
Cash and cash equivalents	$	131,545	$	—
Accounts receivable, net—Westlake Chemical Corporation ("Westlake")	18,529		—
Accounts receivable, net—third parties	37,520		71,812
Inventories	6,634		116,377
Prepaid expenses and other current assets	212		257
Deferred income taxes	—		4,448
Total current assets	194,440		192,894
Property, plant and equipment, net	842,057		762,972
Equity investment	—		10,411
Other assets, net
Goodwill and intangible assets, net	5,814		5,873
Deferred charges and other assets, net	51,919		69,324
Total other assets, net	57,733		75,197
Total assets	$	1,094,230	$	1,041,474
LIABILITIES
Current liabilities
Accounts payable—Westlake	$	5,332	$	—
Accounts payable—third parties	12,348		122,564
Accrued liabilities	11,225		26,688
Total current liabilities	28,905		149,252
Long-term debt payable to Westlake	227,638		252,973
Deferred income taxes	1,848		182,855
Other liabilities	—		962
Total liabilities	258,391		586,042
Commitments and contingencies (Notes 9 and 16)
EQUITY
Net investment	—		455,432
Limited partners interest—Westlake	504,854		—
Limited partner interest—Westlake Chemical Partners LP	330,985		—
Total equity	835,839		455,432
Total liabilities and equity	$	1,094,230	$	1,041,474

The accompanying notes are an integral part of the combined financial statements.

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WESTLAKE CHEMICAL OPCO LP

COMBINED STATEMENTS OF OPERATIONS

	Year Ended December 31,
	2014			2013			2012
				Predecessor			Predecessor
	(in thousands of dollars)
Revenue
Net sales—Westlake	$	1,292,089		$	1,603,043		$	1,507,501
Net co-product, ethylene and feedstock sales—third parties	457,611			524,704			741,597
Total net sales	1,749,700			2,127,747			2,249,098
Cost of sales	1,003,888			1,255,140			1,613,446
Gross profit	745,812			872,607			635,652
Selling, general and administrative expenses	26,870			25,451			24,103
Income from operations	718,942			847,156			611,549
Other income (expense)
Interest expense—Westlake	(10,499		)	(8,032		)	(8,937		)
Other income, net	3,151			7,701			4,186
Income before income taxes	711,594			846,825			606,798
Provision for income taxes	199,388			300,279			210,878
Net income	$	512,206		$	546,546		$	395,920
Less: Predecessor net income prior to initial public    offering on August 4, 2014	361,334
Net income subsequent to initial public offering	$	150,872

The accompanying notes are an integral part of the combined financial statements.

4

WESTLAKE CHEMICAL OPCO LP

COMBINED STATEMENTS OF CHANGES IN EQUITY

	Predecessor			Westlake Chemical OpCo LP
	Net Investment			Limited Partners Interest - Westlake			Limited Partner Interest - Westlake Chemical Partners LP			Total
	(in thousands of dollars)
Balances as of January 1, 2012	$	216,705		$	—		$	—		$	216,705
Net income	395,920			—			—			395,920
Net distributions to Westlake	(338,813		)	—			—			(338,813		)
Balances at December 31, 2012	273,812			—			—			273,812
Contribution of debt payable to Westlake    into net investment	238,600			—			—			238,600
Net income	546,546			—			—			546,546
Net distributions to Westlake	(603,526		)	—			—			(603,526		)
Balances at December 31, 2013	455,432			—			—			455,432
Net income from January 1, 2014 through    August 3, 2014	361,334			—			—			361,334
Net distributions to Westlake prior to    initial public offering	(448,101		)	—			—			(448,101		)
Predecessor net liabilities not assumed by OpCo	239,706			—			—			239,706
Balance as of August 4, 2014 (prior to    initial public offering)	608,371			—			—			608,371
Allocation of net investment to partners' capital	(608,371		)	573,329			35,042			—
Capital contribution from Westlake Chemical    Partners LP	—			—			286,088			286,088
Proceeds from capital contribution from Westlake    Chemical Partners LP distributed to Westlake	—			(151,729		)	—			(151,729		)
Net income from August 4, 2014 through    December 31, 2014	—			134,909			15,963			150,872
Quarterly distribution for the period from    August 4, 2014 to September 30, 2014	—			(51,655		)	(6,108		)	(57,763		)
Balances at December 31, 2014	$	—		$	504,854		$	330,985		$	835,839

The accompanying notes are an integral part of the combined financial statements.

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WESTLAKE CHEMICAL OPCO LP

COMBINED STATEMENTS OF CASH FLOWS

	Year Ended December 31,
	2014			2013			2012
				Predecessor			Predecessor
	(in thousands of dollars)
Cash flows from operating activities
Net income	$	512,206		$	546,546		$	395,920
Adjustments to reconcile net income to net cash provided by operating    activities
Depreciation and amortization	77,611			73,463			64,257
Provision for doubtful accounts	65			40			82
Loss from disposition of fixed assets	1,544			1,905			2,834
Deferred income taxes	8,608			37,054			(8,096		)
Equity in income of joint venture, net of dividends	1,073			402			277
Changes in operating assets and liabilities
Accounts receivable—third parties	(31,551		)	14,352			13,612
Net accounts receivable—Westlake	(13,197		)	—			—
Inventories	24,686			(6,057		)	53,061
Prepaid expenses and other current assets	(624		)	(150		)	164
Accounts payable	(5,181		)	7,362			(34,937		)
Accrued and other liabilities	19,476			(20,852		)	17,717
Other, net	8,588			(51,556		)	(8,070		)
Net cash provided by operating activities	603,304			602,509			496,821
Cash flows from investing activities
Additions to property, plant and equipment	(202,823		)	(223,130		)	(158,440		)
Settlements of derivative instruments	(133		)	(6,920		)	432
Net cash used for investing activities	(202,956		)	(230,050		)	(158,008		)
Cash flows from financing activities
Net distributions to Westlake prior to initial public offering	(448,101		)	(603,526		)	(338,813		)
Repayment of debt payable to Westlake with proceeds from    the capital contribution from Westlake Chemical Partners LP	(78,940		)	—			—
Capital contribution from Westlake Chemical Partners LP	286,088			—			—
Proceeds from capital contribution from Westlake Chemical Partners LP    distributed to Westlake	(151,729		)	—			—
Proceeds from debt payable to Westlake	181,642			231,067			—
Quarterly distribution for the period from August 4, 2014    to September 30, 2014	(57,763		)	—			—
Net cash used for financing activities	(268,803		)	(372,459		)	(338,813		)
Net increase in cash and cash equivalents	131,545			—			—
Cash and cash equivalents at beginning of the year	—			—			—
Cash and cash equivalents at end of the year	$	131,545		$	—		$	—

The accompanying notes are an integral part of the combined financial statements.

6

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS

(in thousands of dollars)

1. Description of Business and Significant Accounting Policies

Description of Business, Formation of Partnership and Initial Public Offering

Westlake Chemical OpCo LP ("OpCo") was formed on May 6, 2014 by Westlake. On August 4, 2014, Westlake Chemical Partners LP (the "Partnership"), a Delaware limited partnership formed in March 2014 to operate, acquire and develop ethylene production facilities and related assets, completed an initial public offering (the "IPO") of 12,937,500 common units representing limited partner interests. In connection with the IPO, the Partnership acquired a 10.6% interest in OpCo and a 100% interest in Westlake Chemical OpCo GP LLC ("OpCo GP"), which is the general partner of OpCo. OpCo owns three ethylene production facilities and a common carrier ethylene pipeline (collectively, the "Contributed Assets"). Westlake retained 89.4% noncontrolling interest in OpCo.

Unless the context otherwise requires, references in these financial statements to the "Predecessor" refer to Westlake Chemical Partners LP Predecessor, the Partnership's and OpCo's predecessor for accounting purposes and refer to the time periods prior to the IPO. References in these financial statements to the Partnership, OpCo and OpCo GP used in the present tense or prospectively refer to the period subsequent to the IPO. References to "Westlake" refer collectively to Westlake Chemical Corporation and its subsidiaries, other than the Partnership, OpCo and OpCo GP.

Prior to the IPO, the Predecessor generated revenue predominantly by selling ethylene and ethylene co-products to Westlake and external customers. The Predecessor typically shipped ethylene, propylene and hydrogen via pipeline systems that connected its ethylene plants to Westlake and numerous third-party customers. The Predecessor transported its butadiene and pyrolysis gasoline by rail or truck.

In connection with the IPO, OpCo and Westlake entered into an ethylene sales agreement (the "Ethylene Sales Agreement") pursuant to which the Partnership generates a substantial majority of its revenue. The Ethylene Sales Agreement has a 12-year initial term and a minimum commitment provision under which Westlake has agreed to purchase 95% of OpCo's planned ethylene production each year, subject to a maximum of 3.8 billion pounds per year. This agreement represents a long-term, minimum-purchase commitment by Westlake with variable pricing equal to OpCo's actual feedstock and natural gas costs and estimated other costs of producing ethylene, plus a fixed margin of $0.10 per pound, less revenue from associated co-product sales. Currently, OpCo expects to sell 95% of its ethylene production to Westlake. For more information, see Note 2 to the combined financial statements.

OpCo sells ethylene production in excess of volumes sold to Westlake, as well as all of the co-products resulting from the ethylene production, including propylene, crude butadiene, pyrolysis gasoline and hydrogen, directly to third parties on either a spot or contract basis. Co-products sold to third parties continue to be transported by rail or truck. Net proceeds (after transportation and other costs) from the sales of ethylene co-products that result from the production of ethylene purchased by Westlake are netted against the ethylene price charged to Westlake under the Ethylene Sales Agreement, thereby reducing OpCo's exposure to fluctuations in the market prices of these co-products.

The Predecessor's operations consisted of the entire ethylene business of Westlake, including the activities of the Contributed Assets, as well as activities which were retained by Westlake. Ethylene business activities retained by Westlake include, but are not limited to, procuring feedstock, managing inventory and commodity risk and transporting ethylene from manufacturing facilities. OpCo's operations consist of activities relating solely to the Contributed Assets.

Basis of Presentation

The accompanying combined financial statements have been prepared in conformity with the accounting principles generally accepted in the United States.

Financial information presented for the periods prior to the IPO consists of the Predecessor's combined financial position as of December 31, 2013, its results of operations, changes in equity and cash flows for the years ended December 31, 2013 and 2012. Financial information of the Predecessor is derived from the financial statements and accounting records of Westlake. Subsequent to the IPO, OpCo's financial position, results of operations and cash flows consist of the activities and balances of OpCo.

7

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

For the year ended December 31, 2014, the results of operations, changes in equity and cash flows include OpCo's results subsequent to the IPO and the Predecessor's combined results prior to the IPO. For these periods, the results of operations and cash flows are referred to as OpCo's results and cash flows.

All financial information presented for the periods after the IPO represents the results of operations, financial position and cash flows of OpCo. Financial information for the periods prior to the IPO represents the combined results of operations, financial position and cash flows of the Predecessor. The combined financial statements were prepared as follows:

• The combined statement of operations for the year ended December 31, 2014 consists of the results of OpCo for the period from August 4, 2014 through December 31, 2014 and the combined results of the Predecessor for the period from January 1, 2014 through August 3, 2014 and for the years ended December 31, 2013 and 2012.

• The balance sheet as of December 31, 2014 consists of the balances of OpCo, while the combined balance sheet as of December 31, 2013 consists of the combined balances of the Predecessor.

• The statement of cash flows for the year ended December 31, 2014 consists of the results of OpCo for the period from August 4, 2014 through December 31, 2014 and the combined results of the Predecessor for the period from January 1, 2014 through August 3, 2014 and for the years ended December 31, 2013 and 2012.

• The statement of changes in equity for the year ended December 31, 2014 consists of the combined activity for the Predecessor prior to August 4, 2014, and the activity for OpCo at and subsequent to the IPO on August 4, 2014 through December 31, 2014. The combined statements of changes in equity for the years ended December 31, 2013 and 2012 consist entirely of the combined activity of the Predecessor.

The combined statements of operations for the periods before August 4, 2014 include expense allocations for certain functions historically performed by Westlake and allocated to the ethylene business, including allocations of general corporate expenses related to finance, legal, information technology, human resources, communications, ethics and compliance, shared services, employee benefits and incentives and stock-based compensation. These allocations were based primarily on direct usage, when identifiable, with the remainder allocated on the basis of fixed assets, headcount or other measures. Management believes the assumptions underlying the combined financial statements, including the assumptions regarding the allocation of expenses from Westlake, are reasonable and reflect all costs related to the operations of the Predecessor, including those incurred by Westlake on behalf of the Predecessor. Nevertheless, the combined financial statements may not include all of the expenses that would have been incurred had the Predecessor been a stand-alone company during the periods presented and may not reflect its results of operations, financial position and cash flows had the Predecessor been a stand-alone company during the periods presented.

With respect to the Predecessor, Westlake used a centralized approach to the cash management and financing of its operations. The cash generated by the Predecessor's operations was transferred to Westlake daily, and Westlake funded the Predecessor's operating and investing activities as needed. Accordingly, the cash and cash equivalents generated by the Predecessor's operations that were held by Westlake were not presented in its combined financial statements for any of the periods presented. The Predecessor reflected transfers of cash to and from Westlake's cash management system as a component of Net investment on its combined balance sheet, and as part of Net distributions to Westlake prior to the initial public offering on its combined statements of cash flows.

Cash and Cash Equivalents

Cash equivalents consist of highly liquid investments that are readily convertible into cash and have a maturity of three months or less at the date of acquisition.

Allowance for Doubtful Accounts

The determination of the allowance for doubtful accounts is based on estimation of the amount of accounts receivable that OpCo believes are unlikely to be collected. Estimating this amount requires analysis of the financial strength of OpCo's customers, the use of historical experience, OpCo's accounts receivable aged trial balance and specific collectability analysis. The allowance for doubtful accounts is reviewed quarterly. Past due balances over 90 days and high risk accounts, as determined by the analysis of financial strength of customers, are reviewed individually for collectability.

8

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

Inventories

Inventories primarily include product, material and supplies. Inventories are stated at the lower of cost or market. Cost is determined using the first-in, first-out ("FIFO") or average method.

Property, Plant and Equipment

Property, plant and equipment are carried at cost, net of accumulated depreciation. Cost includes expenditures for improvements and betterments that extend the useful lives of the assets and interest capitalized on significant capital projects. Historical costs include expenditures for improvements and betterments that extend the useful lives of the assets.

Interest expense is capitalized for qualifying assets under construction. Capitalized interest costs are included in property, plant and equipment and are depreciated over the useful life of the related asset. Capitalized interest was $2,638 for the period from August 4, 2014 to December 31, 2014. Repair and maintenance costs are charged to operations as incurred.

The accounting guidance for asset retirement obligations requires the recording of liabilities equal to the fair value of asset retirement obligations and corresponding additional asset costs, when there is a legal asset retirement obligation as a result of existing or enacted law, statute or contract. OpCo has conditional asset retirement obligations for the removal and disposal of hazardous materials from certain of OpCo's manufacturing facilities. However, no asset retirement obligations have been recognized because the fair value of the conditional legal obligation cannot be measured due to the indeterminate settlement date of the obligation. Settlement of these conditional asset retirement obligations is not expected to have a material adverse effect on OpCo's financial condition, results of operations or cash flows in any individual reporting period.

Depreciation is provided by utilizing the straight-line method over the estimated useful lives of the assets as follows:

Classification	Years
Buildings and improvements	25
Plant and equipment	25
Ethylene pipeline	35
Other	3-10

Impairment of Long-Lived Assets

The accounting guidance for the impairment or disposal of long-lived assets requires that OpCo assess long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable, including when negative conditions such as significant current or projected operating losses exist. Other factors considered by OpCo when determining if an impairment assessment is necessary include, but are not limited to, significant changes or projected changes in supply and demand fundamentals (which would have a negative impact on operating rates or margins), new technological developments, new competitors with significant raw material or other cost advantages, adverse changes associated with the United States and world economies and uncertainties associated with governmental actions. Long-lived assets assessed for impairment are grouped at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to future net undiscounted cash flows expected to be generated by the asset. Assets are considered to be impaired if the carrying amount of an asset exceeds the future undiscounted cash flows. The impairment recognized is measured by the amount by which the carrying amount of the assets exceeds the fair value of the assets. Assets to be disposed of are reported at the lower of the carrying amount or estimated fair value less costs to sell.

Impairment of Intangible Assets

The accounting guidance for goodwill and intangible assets requires that goodwill and indefinite-lived intangible assets are tested for impairment at least annually. Other intangible assets with finite lives are amortized over their estimated useful life and reviewed for impairment in accordance with the provisions of the accounting guidance. As of December 31, 2014, OpCo's recorded goodwill was $5,814. See Note 8 for more information on OpCo's annual goodwill impairment test.

Turnaround Costs

OpCo accounts for turnaround costs under the deferral method. Turnarounds are the scheduled and required shutdowns of specific operating units in order to perform planned major maintenance activities. The costs related to the significant overhaul

9

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

and refurbishment activities include maintenance materials, parts and direct labor costs. The costs of the turnaround are deferred when incurred at the time of the turnaround and amortized (within depreciation and amortization) on a straight-line basis until the next planned turnaround, which ranges from three to six years. Deferred turnaround costs are presented as a component of other assets, net. The cash outflows related to these costs are included in operating activities in the combined statements of cash flows.

Exchanges

OpCo enters into inventory exchange transactions with respect to ethylene. These exchanges are settled in like-kind quantities and are valued at lower of cost or market. The Predecessor entered into inventory exchange transactions with third parties, which involve fungible commodities. These exchanges are settled in like-kind quantities and are valued at lower of cost or market. Cost is determined using the FIFO method.

Concentration of Credit Risk

Financial instruments which potentially subject OpCo to concentration of risk consist principally of trade receivables from third-party customers who purchase ethylene and ethylene co-products. OpCo performs periodic credit evaluations, as applicable, of the customers' financial condition and generally does not require collateral. OpCo maintains allowances for potential losses, as applicable.

Revenue Recognition

Revenue is recognized when persuasive evidence of an arrangement exists, products are delivered to the customer, the sales price is fixed or determinable, and collectability is reasonably assured. Title and risk of loss passes to the customer upon delivery under executed customer purchase orders or contracts. Provisions for discounts, rebates and returns are provided for in the same period as the related sales are recorded.

Price Risk Management

The accounting guidance for derivative instruments and hedging activities requires that OpCo and the Predecessor recognize all derivative instruments on the balance sheet at fair value, and changes in the derivative's fair value must be currently recognized in earnings or comprehensive income, depending on the designation of the derivative. If the derivative is designated as a fair value hedge, the changes in the fair value of the derivative and of the hedged item attributable to the hedged risk are recognized in earnings. If the derivative is designated as a cash flow hedge, the effective portion of the change in the fair value of the derivative is recorded in comprehensive income and is recognized in the statement of operations when the hedged item affects earnings. Ineffective portions of changes in the fair value of cash flow hedges are recognized in earnings currently. During the years presented, neither OpCo nor the Predecessor had cash flow hedges.

The Predecessor utilized commodity derivative instruments to reduce price risks by purchasing or selling futures on established exchanges. The Predecessor took both fixed and variable positions, depending upon anticipated future physical purchases and sales of these commodities. The fair value of derivative financial instruments was estimated using quoted market prices in active markets and observable market-based inputs or unobservable inputs that were corroborated by market data when active markets were not available. The Predecessor assessed both counterparty as well as its own nonperformance risk when measuring the fair value of derivative liabilities. The Predecessor did not consider its nonperformance risk to be significant. See Note 12 for a summary of the fair value of derivative instruments. OpCo did not enter into such instruments in 2014 since the date of the IPO.

Environmental Costs

Environmental costs relating to current operations are expensed or capitalized, as appropriate, depending on whether such costs provide future economic benefits. Remediation liabilities are recognized when the costs are considered probable and can be reasonably estimated. Measurement of liabilities is based on currently enacted laws and regulations, existing technology and undiscounted site-specific costs. Environmental liabilities in connection with properties that are sold or closed are realized upon such sale or closure, to the extent they are probable and estimable and not previously reserved. Recognition of any joint and several liabilities is based upon OpCo's best estimate of its final pro rata share of the liability.

10

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

Fair Value of Financial Instruments

The amounts reported in the combined balance sheets for cash and cash equivalents, accounts receivable, net and accounts payable approximate their fair value due to the short maturities of these instruments. The fair value of OpCo's senior unsecured revolving credit facility and OpCo's promissory notes payable to Westlake, which were assumed by OpCo in connection with the IPO (the "August 2013 Promissory Notes"), at December 31, 2014, approximates the fair value due to the variable nature of the interest rate. The fair value of financial instruments is estimated using quoted market prices in active markets and observable market-based inputs or unobservable inputs that are corroborated by market data when active markets are not available. See Note 12 for more information on the fair value of financial instruments.

Income Taxes

OpCo is a limited partnership and is treated as a partnership for U.S. federal income tax purposes and, therefore, is not liable for entity-level federal income taxes. OpCo is, however, subject to state and local income taxes. The Predecessor's operating results were included in Westlake's consolidated U.S. federal and state income tax returns. Amounts presented in the combined financial statements prior to the IPO relate to income taxes that have been determined on a separate tax return basis, and the Predecessor's contribution to Westlake Chemical Corporation's net operating losses and tax credits have been included in the Predecessor's financial statements. The Predecessor utilized the liability method of accounting for deferred income taxes. Under the liability method, deferred tax assets or liabilities are recorded based upon temporary differences between the tax basis of assets and liabilities and their carrying values for financial reporting purposes. Deferred tax expense or benefit is the result of changes in the deferred tax assets and liabilities during the period. Valuation allowances were recorded against deferred tax assets when it was considered more likely than not that the deferred tax assets will not be realized on a separate tax return basis.

Employee Benefit Plans

The employees supporting the Predecessor's operations were employees of Westlake and its affiliates. Their payroll costs and employee benefit plan costs were charged to the Predecessor by Westlake. Westlake sponsors various employee pension and postretirement health and life insurance plans. The Predecessor was considered to have participated in multiemployer benefit plans of Westlake. As a participant in multiemployer benefit plans, the Predecessor recognized as expense in each period an allocation from Westlake, and the Predecessor did not recognize any employee benefit plan assets or liabilities except for accruals for contributions due.

Use of Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, and the disclosure of contingent assets and liabilities. Actual results could differ from those estimates.

Net Investment

In the combined balance sheets, Net investment represents Westlake's historical investment in the Predecessor, its accumulated net earnings after taxes, and the net effect of transactions with, and allocations from, Westlake.

Other Assets

Certain other assets (see Note 8) are amortized over periods ranging from five to 20 years using the straight-line method.

Comprehensive Income

OpCo has reported no comprehensive income due to the absence of items of other comprehensive income in the years presented.

11

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

2. Initial Public Offering

Contributed Assets

In connection with the IPO, the Partnership acquired a 10.6% interest in OpCo and a 100% interest in OpCo GP. OpCo owns the Contributed Assets.

Other assets contributed to OpCo in conjunction with the IPO include the deferred turnaround costs associated with Lake Charles Olefins and Calvert City Olefins, co-product inventories, goodwill and other assets. Additionally, OpCo assumed the August 2013 Promissory Notes in the amount of $246,056.

The Predecessor's combined financial statements reflect certain assets, liabilities and business activities that were retained by Westlake and, therefore, are not reflected in OpCo's combined financial statements. Assets and liabilities which are reflected in the Predecessor's combined financial statements but which were retained by Westlake include working capital accounts, ethylene and other inventories, an equity interest in a pipeline joint venture, deferred federal income taxes, certain long-term debt payable to Westlake and other long-term liabilities. Ethylene business activities retained by Westlake include, but are not limited to, procuring feedstock, managing inventory and commodity risk and transporting ethylene from manufacturing facilities. See Note 14 for details of the Predecessor's net liabilities retained by Westlake.

Initial Public Offering

On August 4, 2014, the Partnership completed the IPO of 12,937,500 common units at a price to the public of $24.00 per unit ($22.53 per unit net of underwriting discount), including 1,687,500 common units that were issued pursuant to the exercise in full of the underwriters' over-allotment option.

In connection with the IPO, in exchange for Westlake's contribution of a 5.8% limited partner interest in OpCo and OpCo's general partner interest to the Partnership, Westlake received:

• 1,436,115 common units and 12,686,115 subordinated units; and

• the Partnership's general partner interest and its incentive distribution rights.

The Partnership received net proceeds of $286,088 from the IPO, net of underwriting discounts, structuring fees and offering expenses of approximately $24,412. The Partnership used the net proceeds from the IPO to purchase an additional 4.8% limited partner interest in OpCo, resulting in the Partnership owning a 10.6% limited partner interest in OpCo.

From the period beginning August 4, 2012 to July 31, 2013, Westlake incurred approximately $151,729 in capital expenditures (the "Pre-August 2013 Capex") with respect to the assets contributed to OpCo. The portion of these capital expenditures incurred before January 1, 2013 was accounted for as an adjustment to Net investment, as it was funded through equity. The portion of the capital expenditures incurred from January 1, 2013 through July 31, 2013 was accounted for as a liability and is reflected as such on the Predecessor's combined financial statements, and the associated liability was retained by Westlake in connection with the IPO. During the period from August 1, 2013 through August 3, 2014, Westlake funded capital expenditures of $246,056 related to the Contributed Assets under the terms of the August 2013 Promissory Notes. At the close of the IPO, the outstanding balance of the August 2013 Promissory Notes was $246,056.

OpCo used the $286,088 it received from the Partnership in exchange for a 4.8% limited partner interest in OpCo to (1) establish a $55,419 turnaround reserve, (2) reimburse Westlake $151,729 for the Pre-August 2013 Capex, and (3) repay $78,940 of the August 2013 Promissory Notes assumed by OpCo. Immediately after the repayment, the outstanding indebtedness payable to Westlake under the August 2013 Promissory Notes was $167,116.

Agreements with Westlake and Related Parties

The agreements described below became effective on August 4, 2014, concurrent with the closing of the IPO.

Ethylene Sales Agreement

OpCo entered into a 12-year ethylene sales agreement with Westlake (the "Ethylene Sales Agreement"). The Ethylene Sales Agreement requires Westlake to purchase a minimum volume of ethylene each year equal to 95% of OpCo's planned ethylene production per year (the "Minimum Commitment"), subject to certain exceptions and a maximum commitment of 3.8 billion pounds per year. So long as Westlake is not in default under the Ethylene Sales Agreement, if OpCo's actual production

12

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

exceeds planned production, Westlake has the option to purchase up to 95% of the excess production (the "Excess Production Option").

The fee for each pound of ethylene purchased by Westlake from OpCo up to the Minimum Commitment in any calendar year will equal:

• the actual price OpCo pays Westlake to purchase ethane (or other feedstock, such as propane, if applicable) to produce each pound of ethylene, subject to a specified cap and a floor on the amount of feedstock that should be needed to produce each pound of ethylene; plus

• the actual price OpCo pays Westlake to purchase natural gas to produce each pound of ethylene, subject to a specified cap and a floor on the amount of natural gas that should be needed to produce each pound of ethylene; plus

• OpCo's estimated operating costs (including selling, general and administrative expenses), divided by OpCo's planned ethylene production for the year (in pounds); plus

• a five-year average of OpCo's expected future maintenance capital expenditures and other turnaround expenditures, divided by OpCo's planned ethylene production capacity for the year (in pounds); less

• the proceeds (on a per pound of ethylene basis) received by OpCo from the sale of co-products (including, but not limited to, propylene, crude butadiene, pyrolysis gasoline and hydrogen) associated with producing the ethylene purchased by Westlake; plus

• a $0.10 per pound margin.

The fee for the Excess Production Option, if exercised, equals OpCo's estimated variable operating costs of producing the incremental ethylene, net of revenues from co-product sales plus a $0.10 per pound margin.

The estimated operating costs and the expected future maintenance capital expenditures and other turnaround expenditures will be adjusted at the end of each year, to be applicable for the fee for the next calendar year, to reflect certain changes in forecasted costs.

The result of the fee structure is that OpCo should recover the portion of its total operating costs and maintenance capital expenditures and other turnaround expenditures corresponding to the portion of OpCo's aggregate production that is purchased by Westlake. The Ethylene Sales Agreement has an initial term extending until December 31, 2026 and automatically renews thereafter for successive 12-month terms unless terminated.

Feedstock Supply Agreement

OpCo entered into a feedstock supply agreement with Westlake, pursuant to which Westlake agreed to sell to OpCo ethane and other feedstock in amounts sufficient for OpCo to produce the ethylene to be sold under the Ethylene Sales Agreement (the "Feedstock Supply Agreement"). The Feedstock Supply Agreement provides that OpCo may obtain feedstock from Westlake based on Westlake's total cost of purchasing and delivering the feedstock, including applicable transportation, storage and other costs. Title and risk of loss for all feedstock purchased by OpCo through the Feedstock Supply Agreement passes to OpCo upon delivery to one of three delivery points described in the Feedstock Supply Agreement.

The Feedstock Supply Agreement has an initial term extending until December 31, 2026 and automatically renews thereafter for successive 12-month terms unless terminated by either party; provided, however, that such agreement can only be renewed in the event the Ethylene Sales Agreement is renewed simultaneously. The Feedstock Supply Agreement may, in certain circumstances, terminate concurrently with the termination of the Ethylene Sales Agreement.

Services and Secondment Agreement

OpCo entered into a services and secondment agreement with Westlake, pursuant to which OpCo provides Westlake with certain services required for the operation of Westlake's facilities; and Westlake provides OpCo with comprehensive operating services for OpCo's facilities, ranging from services relating to the maintenance and operations of the common facilities necessary for the operation of OpCo's units, to making available certain shared utilities such as electricity and natural gas that are necessary for the operation of OpCo's units. Westlake also seconds employees to OpCo to allow OpCo to operate its facilities. Such seconded employees will be under the control of OpCo while they work on OpCo's facilities.

The services and secondment agreement has an initial 12-year term. The services and secondment agreement may be renewed thereafter upon agreement of the parties and shall automatically terminate if the Ethylene Sales Agreement terminates

13

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

under certain circumstances. Westlake and OpCo each can terminate the services and secondment agreement under certain circumstances, including if the other party materially defaults on the performance of its obligations and such default continues for a 30-day period.

Site Lease Agreements

OpCo entered into two site lease agreements with Westlake pursuant to which Westlake leases to OpCo the real property underlying Lake Charles Olefins and Calvert City Olefins, respectively, and grants OpCo rights to access and use certain other portions of Westlake's ethylene production facilities that are necessary to operate OpCo's production facilities. OpCo owes Westlake one dollar per site per year. The site lease agreements each have a term of 50 years. Each of the site lease agreements may be renewed if agreed by the parties.

Omnibus Agreement

OpCo, the Partnership and certain related parties entered into an omnibus agreement with Westlake that addresses (1) Westlake's indemnification of OpCo and the Partnership for certain matters, including environmental and tax matters, (2) the provision by Westlake of certain management and other general and administrative services to OpCo and the Partnership and its general partner and (3) OpCo and the Partnership's reimbursement to Westlake for such services. The omnibus agreement also addresses Westlake's right of first refusal on any proposed transfer of the ethylene production facilities that serve Westlake's other facilities and Westlake's right of first refusal on any proposed transfer of the Partnership's equity interests in OpCo.

3. Recent Accounting Pronouncements

Revenue from Contracts with Customers

In May 2014, the Financial Accounting Standards Board ("FASB") issued an accounting standards update on a comprehensive new revenue recognition standard that will supersede the existing revenue recognition guidance. The new accounting guidance creates a framework by which an entity will allocate the transaction price to separate performance obligations and recognize revenue when each performance obligation is satisfied. Under the new standard, entities will be required to use judgment and make estimates, including identifying performance obligations in a contract, estimating the amount of variable consideration to include in the transaction price, allocating the transaction price to each separate performance obligation and determining when an entity satisfies its performance obligations. The standard allows for either "full retrospective" adoption, meaning that the standard is applied to all of the periods presented with a cumulative catch-up as of the earliest period presented, or "modified retrospective" adoption, meaning the standard is applied only to the most current period presented in the financial statements with a cumulative catch-up as of the current period. The accounting standard will be effective for reporting periods beginning after December 15, 2016. OpCo is in the process of evaluating the impact that the new accounting guidance will have on its financial position, results of operations and cash flows.

Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern

In August 2014, the FASB issued an accounting standards update on management's responsibility to evaluate whether there is substantial doubt about an entity's ability to continue as a going concern. The new accounting guidance requires management to perform interim and annual assessments of an entity's ability to continue as a going concern within one year of the date the financial statements are issued. An entity must provide certain disclosures if "conditions or events raise substantial doubt about the entity's ability to continue as a going concern." The accounting standard will be effective for reporting periods ending after December 15, 2016 and is not expected to have an impact on OpCo's financial position, results of operations and cash flows.

4. Financial Instruments

Cash Equivalents

OpCo had $40,003 of held-to-maturity securities with original maturities of three months or less, primarily consisting of corporate debt securities, classified as cash equivalents at December 31, 2014. OpCo's investments in held-to-maturity securities are held at amortized cost, which approximates fair value.

14

5. Accounts Receivable—Third Parties

Accounts receivable—third parties consist of the following:

	December 31,
	2014		2013
			Predecessor
Trade customers	$	37,514	$	73,594
Allowance for doubtful accounts	—		(2,105		)
	37,514		71,489
Other	6		323
Accounts receivable, net—third parties	$	37,520	$	71,812

6. Inventories

Inventories consist of the following:

	December 31,
	2014		2013
			Predecessor
Finished products	$	6,257	$	21,330
Feedstock, additives and chemicals	377		80,407
Materials and supplies	—		14,640
Inventories	$	6,634	$	116,377

7. Property, Plant and Equipment

Property, plant and equipment consist of the following:

	December 31,
	2014			2013
				Predecessor
Land	$	—		$	4,126
Building and improvements	14,961			32,941
Plant and equipment	1,151,091			1,058,304
Other	61,533			55,478
	1,227,585			1,150,849
Less: Accumulated depreciation	(550,568		)	(561,301		)
	677,017			589,548
Construction in progress	165,040			173,424
Property, plant and equipment, net	$	842,057		$	762,972

Depreciation expense on property, plant and equipment of $60,004, $57,299 and $53,125 is included in cost of sales in the combined statements of operations for the years ended December 31, 2014, 2013 and 2012, respectively.

15

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

8. Other Assets

Other assets consist of the following:

	December 31, 2014							December 31, 2013							Weighted Average Life
								Predecessor
	Cost		Accumulated Amortization			Net		Cost		Accumulated Amortization			Net
Intangible assets:
Technology	$	—	$	—		$	—	$	9,618	$	(9,618	)	$	—
Goodwill	5,814		—			5,814		5,814		—			5,814
Other	—		—			—		59		—			59
Total intangible assets	5,814		—			5,814		15,491		(9,618		)	5,873
Turnaround costs	96,835		(51,536		)	45,299		96,678		(34,537		)	62,141		5
Other	8,662		(2,042		)	6,620		8,662		(1,479		)	7,183		15
Total deferred charges and    other assets	105,497		(53,578		)	51,919		105,340		(36,016		)	69,324
Other assets, net	$	111,311	$	(53,578	)	$	57,733	$	120,831	$	(45,634	)	$	75,197

Amortization expense on other assets of $17,607, $16,164 and $11,132 is included in the combined statements of operations for the years ended December 31, 2014, 2013 and 2012, respectively.

At December 31, 2014, there were no scheduled amortizations of intangible assets in the next five years.

Goodwill

There was no change in the carrying amount of goodwill during 2014.

The impairment test for the recorded goodwill was performed in October 2014 and did not indicate impairment of the goodwill. The fair value of the goodwill was calculated using both a discounted cash flow methodology and a market value methodology. The discounted cash flow projections were based on a nine-year forecast, from 2015 to 2023, to reflect the cyclicality of OpCo's business. The forecast was based on (1) prices and spreads projected by IHS Chemical, a chemical industry organization offering market and business advisory services for the chemical market, for the same period, and (2) estimates by management, including their strategic and operational plans. Other significant assumptions used in the discounted cash flow projection included sales volumes based on current capacities. The future cash flows were discounted to present value using a discount rate of 8.8%. The significant assumptions used in determining the fair value of the reporting unit using the market value methodology include the determination of appropriate market comparables and the estimated multiples of EBITDA a willing buyer is likely to pay. Under the discounted cash flow methodology, even if the fair value of OpCo decreased by 10%, the carrying value of OpCo would not exceed its fair value.

9. Long-Term Debt

Long-term debt consists of the following:

	December 31,
	2014		2013
			Predecessor
2006 Pipeline Note (variable interest rate of prime plus 0.25%, original scheduled    maturity of November 30, 2016)	$	—	$	14,400
August 2013 Promissory Notes (variable interest rate of prime plus 1.5%, original    scheduled maturity of August 1, 2023)	167,116		238,573
Senior unsecured revolving credit facility (variable interest rate of LIBOR plus 3.0%,    original scheduled maturity of August 4, 2019)	60,522		—
Long-term debt payable to Westlake	$	227,638	$	252,973

In 2013, the August 2013 Promissory Notes were issued for capital expenditures incurred by Westlake on behalf of the Predecessor's operations. Proceeds drawn under the August 2013 Promissory Notes during 2014 were used to fund capital

16

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

expenditures at the Predecessor's ethylene plants. In connection with the IPO, OpCo assumed the August 2013 Promissory Notes and used proceeds from the IPO to repay a portion of the balance it assumed. See Note 2 for a description of the August 2013 Promissory Notes and proceeds used to repay balances of such promissory notes assumed in connection with the IPO.

In connection with the IPO on August 4, 2014, OpCo entered into a senior unsecured revolving credit facility with Westlake. The credit facility accrues interest quarterly at a rate of LIBOR plus 3.0%, which may be paid-in-kind as an addition to the principal at OpCo's option.

As of December 31, 2014, OpCo was in compliance with all of the covenants with respect to the August 2013 Promissory Notes and the revolving credit facility.

The weighted average interest rate on all long-term debt was 4.35% and 4.69% at December 31, 2014 and 2013, respectively.

As of December 31, 2014, OpCo had no maturities of long-term debt until 2019. OpCo's revolving credit facility matures on August 4, 2019, and the August 2013 Promissory Notes mature on August 1, 2023.

10.Related Party Transactions

OpCo regularly enters into related party transactions with Westlake. See below for a description of transactions with related parties.

Sales to Related Parties

OpCo sells ethylene to Westlake under the Ethylene Sales Agreement. Additionally, OpCo from time to time provides other services or products for which it charges Westlake a fee. Prior to the IPO, the Predecessor sold the majority of its ethylene to Westlake for use in Westlake's downstream operations.

Sales to related parties were as follows:

	Year Ended December 31,
	2014		2013		2012
			Predecessor		Predecessor
Net sales—Westlake	$	1,292,089	$	1,603,043	$	1,507,501

Cost of Sales from Related Parties

Charges for goods and services purchased by OpCo from Westlake and included in cost of sales relate primarily to feedstock purchased under the Feedstock Supply Agreement and services provided under the services and secondment agreement. Prior to the IPO, services provided by Westlake and included in cost of sales related primarily to services provided by employees of Westlake Management Services, Inc., a subsidiary of Westlake. The cost of services provided by employees of Westlake Management Services, Inc. was allocated to the Predecessor's operations primarily on the basis of direct usage.

Charges from related parties in cost of sales were as follows:

	Year Ended December 31,
	2014		2013		2012
			Predecessor		Predecessor
Feedstock purchased from Westlake and included in cost of sales	$	155,232	$	—	$	—
Other charges from Westlake and included in cost of sales	60,264		61,770		57,454
Total	$	215,496	$	61,770	$	57,454

Services from Related Parties Included in Selling, General and Administrative Expenses

Charges for services purchased by OpCo from Westlake and included in selling, general and administrative expenses primarily relate to services Westlake performs on behalf of OpCo under the Omnibus Agreement, including OpCo's finance, legal, information technology, human resources, communication, ethics and compliance and other administrative functions. Prior to the IPO, the Predecessor was allocated costs incurred by Westlake on its behalf for similar functions. These allocations

17

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

were based primarily on the basis of direct usage when identifiable, with the remainder allocated on the basis of fixed assets, headcount or other measure.

Charges from related parties included within selling, general and administrative expenses were as follows:

	Year Ended December 31,
	2014		2013		2012
			Predecessor		Predecessor
Services received from Westlake and included in selling,    general and administrative expenses	$	20,420	$	24,054	$	22,485

Goods and Services from Related Parties Capitalized as Assets

Charges for goods and services purchased by OpCo from Westlake which were capitalized as assets relate primarily to the services of Westlake employees under the Services and Secondment Agreement. Prior to the IPO, salaries and benefits of Westlake Management Services, Inc. were allocated to the Predecessor primarily on the basis of direct usage.

Charges from related parties for goods and services capitalized as assets were as follows:

	Year Ended December 31,
	2014		2013		2012
			Predecessor		Predecessor
Goods and services purchased from Westlake and capitalized as assets	$	5,823	$	20,222	$	8,902

Accounts Receivable from and Accounts Payable to Related Parties

OpCo's accounts receivable from Westlake result primarily from ethylene sales to Westlake under the Ethylene Sales Agreement. OpCo's accounts payable to Westlake result primarily from feedstock purchases under the Feedstock Supply Agreement and services provided under the Services and Secondment agreement and the omnibus agreement. Prior to the IPO, ethylene sales and other transactions between the Predecessor and Westlake were settled immediately through net investment and, therefore, the Predecessor did not have related party accounts receivable or related party accounts payable balances.

The related party accounts receivable and accounts payable balances were as follows:

	December 31,
	2014		2013
			Predecessor
Accounts receivable, net—Westlake	$	18,529	$	—
Accounts payable—Westlake	5,332		—

Debt Payable to Related Parties

OpCo assumed the August 2013 Promissory Notes and entered into a senior unsecured revolving credit facility with Westlake in connection with the IPO. Prior to the IPO, the Predecessor funded certain capital expenditures through the August 2013 Promissory Notes payable to Westlake which were assumed by OpCo in connection with the IPO. See Note 9 for a description of related party debt payable balances. Interest capitalized as a component of property, plant and equipment on related party debt was $2,638 for the period from August 4, 2014 to December 31, 2014. At December 31, 2014 and 2013, accrued interest on related party debt was $2,403 and $504, respectively, and is reflected as a component of accrued liabilities. Additionally, at December 31, 2013, accrued interest of $7,506 was included as a component of the outstanding debt payable to Westlake.

Debt payable to related parties was as follows:

	December 31,
	2014		2013
			Predecessor
Long-term debt payable to Westlake	$	227,638	$	252,973

18

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

General

OpCo, together with other subsidiaries of Westlake not included in these combined financial statements, are guarantors under Westlake's revolving credit facility and the indentures governing its senior notes. As of December 31, 2014, Westlake had outstanding letters of credit totaling $31,392 under its revolving credit facility and $754,000 principal amount outstanding under its senior notes (less the unamortized discount of $892).

The indentures governing Westlake's senior notes prevent OpCo from making distributions to the Partnership if any default or event of default (as defined in the indentures) exists. However, Westlake's credit facility does not prevent OpCo from making distributions to the Partnership.

Westlake uses a centralized cash management system to finance its operations. Interest paid, net of capitalized interest, and income taxes have been paid directly by Westlake and charged to the Predecessor through related party accounts receivable, net. Related party accounts receivable, net were settled immediately through net investment, and therefore, the Predecessor did not pay cash for interest expense or income tax expense during the years ended December 31, 2013 or 2012.

OpCo has entered into two site lease agreements with Westlake in connection with the IPO, and each has a term of 50 years. Pursuant to the site lease agreements, OpCo pays Westlake one dollar per site per year.

11. Derivative Commodity Instruments

Commodity Risk Management

The Predecessor used derivative instruments to reduce price volatility risk on raw materials and products, as a substantial portion of its raw materials and products were commodities whose prices fluctuate as market supply and demand fundamentals change. The Predecessor employed strategies to protect against such instability, including ethylene product feedstock flexibility. The Predecessor did not use derivative instruments to engage in speculative activities. The Contributed Assets do not include the entity engaged in commodity risk management activities or any of its open derivative positions. OpCo has not engaged in any hedging activity and did not use derivative instruments in the period subsequent to the IPO through December 31, 2014. Therefore, there are no derivative assets or liabilities reflected in the balance sheet of OpCo as of December 3l, 2014.

For derivative instruments that are designated and qualify as fair value hedges, the gains or losses on the derivative instruments, as well as the offsetting losses or gains on the hedged items attributable to the hedged risk, were included in cost of sales in the combined statements of operations for the years ended December 31, 2014, 2013 and 2012. OpCo had no derivative instruments that were designated as fair value hedges subsequent to the IPO through December 31, 2014.

Gains and losses from changes in the fair value of derivative instruments that are not designated as hedging instruments were included in gross profit in the combined statements of operations for the years ended December 31, 2014, 2013 and 2012. OpCo had no derivative instruments that were not designated as hedging instruments subsequent to the IPO through December 31, 2014.

The exposure on commodity derivatives used for price risk management includes the risk that the counterparty will not pay if the market declines below the established fixed price. In such case, the derivative holder would lose the benefit of the derivative differential on the volume of the commodities covered. In any event, the derivative holders would continue to receive the market price on the actual volume hedged. Derivative holders also bear the risk of losing the benefit of market improvements over the fixed derivative price for the term and volume of the derivative instruments (as such improvements would accrue to the benefit of the counterparty).

Disclosures related to the Predecessor's derivative assets and derivative liabilities subject to enforceable master netting arrangements have not been presented as they were not material to the Predecessor's combined balance sheet at December 31, 2013. There was no open derivative position at December 31, 2014.

19

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

The fair values of derivative instruments in the combined balance sheets were as follows:

	Asset Derivatives
	Balance Sheet Location	Fair Value as of December 31,
		2014		2013
				Predecessor
Not designated as hedging instruments
Commodity forward contracts	Accounts receivable, net	$	—	$	296
Total asset derivatives		$	—	$	296
	Liability Derivatives
	Balance Sheet Location	Fair Value as of December 31,
		2014		2013
				Predecessor
Not designated as hedging instruments
Commodity forward contracts	Accrued liabilities	$	—	$	176
Total liability derivatives		$	—	$	176

The following tables reflect the impact of derivative instruments designated as fair value hedges and the related hedged item on the combined statements of operations. There was no material ineffectiveness with regard to the Predecessor's qualifying hedges in 2013 and 2012.

Derivatives in Fair Value    Hedging Relationships	Location of Gain (Loss) Recognized in Income on Derivative	Year Ended December 31,
		2014		2013			2012
				Predecessor			Predecessor
Commodity forward contracts	Cost of sales	$	—	$	(303	)	$	17,163

Hedged Items in Fair Value    Hedging Relationships	Location of Gain (Loss) Recognized in Income on  Hedged Items	Year Ended December 31,
		2014		2013		2012
				Predecessor		Predecessor
Firm commitment designated as the    hedged item	Cost of sales	$	—	$	143	$	(18,394	)

The impact of derivative instruments that have not been designated as hedges in the combined statements of operations were as follows:

Derivatives Not Designated as    Hedging Instruments	Location of Gain (Loss) Recognized in Income on Derivative	Year Ended December 31,
		2014			2013		2012
					Predecessor		Predecessor
Commodity forward contracts	Gross profit	$	(9,244	)	$	5,438	$	(11,961	)

See Note 12 for the fair value of derivative instruments.

12. Fair Value Measurements

OpCo reports certain assets and liabilities at fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). Under the accounting guidance for fair value measurements, inputs used to measure fair value are classified in one of three levels:

Level 1: Quoted market prices in active markets for identical assets or liabilities.

Level 2: Observable market-based inputs or unobservable inputs that are corroborated by market data.

Level 3: Unobservable inputs that are not corroborated by market data.

20

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

There were no assets or liabilities accounted for at fair value on a recurring basis as of December 31, 2014. The following table summarizes, by level within the fair value hierarchy, the Predecessor's assets and liabilities that were accounted for at fair value on a recurring basis at December 31, 2013:

	December 31, 2013
	Level 1		Level 2			Total
	Predecessor
Derivative instruments
Risk management assets - Commodity forward contracts	$	48	$	248		$	296
Risk management liabilities - Commodity forward contracts	—		(176		)	(176		)

The Level 2 measurements for the Predecessor's commodity contracts are derived using forward curves supplied by industry recognized and unrelated third-party services. There were no transfers in and out of Levels 1 and 2 of the fair value hierarchy during 2014 and 2013.

OpCo has other financial assets and liabilities subject to fair value measures. These financial assets and liabilities include cash and cash equivalents, accounts receivable, net, accounts payable and long-term debt, all of which are recorded at carrying value. The amounts reported in the combined balance sheets for cash and cash equivalents, accounts receivable, net and accounts payable approximate their fair value due to the short maturities of these instruments. The carrying and fair values of OpCo's and the Predecessor's long-term debt at December 31, 2014 and 2013 are summarized in the table below. OpCo's long-term debt includes the August 2013 Promissory Notes and the senior unsecured revolving credit facility. The fair value of debt is determined based on the present value of expected future cash flows using a discounted cash flow methodology. Because OpCo's valuation methodology used for long-term debt requires the use of significant unobservable inputs, the inputs used to measure the fair value of OpCo's long-term debt are classified as Level 3 within the fair value hierarchy. Inputs used to estimate the fair values of OpCo's long-term debt include the selection of an appropriate discount rate.

	December 31, 2014				December 31, 2013
	Carrying Value		Fair Value		Carrying Value		Fair Value
					Predecessor
2006 Pipeline Note	$	—	$	—	$	14,400	$	13,922
August 2013 Promissory Notes	167,116		167,116		238,573		238,573
Senior unsecured revolving credit facility	60,522		60,522		—		—

13. Income Taxes

OpCo is a limited partnership and is treated as a partnership for U.S. federal income tax purposes and, therefore, is not liable for entity-level federal income taxes. OpCo is, however, subject to state and local income taxes. The Predecessor's operating results were included in Westlake's consolidated U.S. federal and state income tax returns. Amounts presented in the combined financial statements prior to the IPO relate to income taxes that have been determined on a separate tax return basis and the Predecessor's contribution to Westlake Chemical Corporation's net operating losses and tax credits have been included in the Predecessor's financial statements.

21

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

The components of income tax disaggregated between OpCo and the Predecessor are as follows:

	OpCo		Predecessor
	Period from August 4, 2014 to December 31, 2014		Period from January 1, 2014 to August 3, 2014		Year Ended December 31,
						2013		2012
Current
Federal	$	—	$	168,773		$	233,014	$	196,467
State and Local	800		21,207			30,211		22,507
	800		189,980			263,225		218,974
Deferred
Federal	—		6,890			32,675		(8,137		)
State and Local	265		1,453			4,379		41
	265		8,343			37,054		(8,096		)
Total provision	$	1,065	$	198,323		$	300,279	$	210,878

The reconciliation of income tax expense at the U.S. statutory rate to the income tax expense disaggregated between OpCo and the Predecessor is as follows:

	OpCo			Predecessor
	Period from August 4, 2014 to December 31, 2014			Period from January 1, 2014 to August 3, 2014			Year Ended December 31,
								2013			2012
Provision for federal income tax, at statutory rate	$	53,178		$	195,880			$	296,389		$	212,379
State income tax provision, net of federal income tax    effect	1,065			14,729				22,484			14,656
Partnership income not subject to entity-level tax	(53,178		)	—				—			—
Manufacturing deduction	—			(12,214		)		(18,270		)	(16,065		)
Other, net	—			(72		)		(324		)	(92		)
	$	1,065		$	198,323			$	300,279		$	210,878

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WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

The tax effects of the principal temporary differences between financial reporting and income tax reporting are as follows:

	December 31,
	2014			2013
				Predecessor
Credit carryforward	$	—		$	25
Accruals	—			3,570
Allowance for doubtful accounts	—			(136		)
Inventories	—			1,313
Other	—			(373		)
Deferred taxes assets—total	—			4,399
Property, plant and equipment	(1,650		)	(159,033		)
Turnaround costs	(198		)	(23,773		)
Deferred tax liabilities—total	(1,848		)	(182,806		)
Total net deferred tax liabilities	$	(1,848	)	$	(178,407	)
Balance sheet classifications
Current deferred tax asset	$	—		$	4,448
Noncurrent deferred tax liability	(1,848		)	(182,855		)
Total net deferred tax liabilities	$	(1,848	)	$	(178,407	)

14. Supplemental Information

Net Liabilities Retained by Westlake

Net liabilities of the Predecessor that were retained by Westlake and not assumed by OpCo in connection with the IPO are composed of the following:

Net liabilities retained by Westlake
Accounts receivable, net—third parties	$	64,650
Inventories	85,057
Prepaid expenses and other current assets	669
Deferred income taxes	4,448
Property, plant and equipment, net	62,886
Equity investments	9,338
Accounts payable—third parties	(101,671		)
Accrued liabilities	(37,451		)
Deferred income taxes	(189,615		)
Long-term debt	(137,103		)
Other assets (liabilities)	(914		)
Total	$	(239,706	)

Accrued Liabilities

Accrued liabilities were $11,225 and $26,688 at December 31, 2014 and 2013, respectively. Accrued taxes, interest accrued on long-term debt and accrual related to capital expenditures, which are components of accrued liabilities, were $1,622, $2,403 and $5,026 at December 31, 2014, respectively. Accrued employee payroll and benefits, which is a component of accrued liabilities, was $10,598 at December 31, 2013. No other component of accrued liabilities was more than five percent of total current liabilities.

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WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

Other Income, Net

	Year Ended December 31,
	2014			2013			2012
				Predecessor			Predecessor
Income from equity method investments	$	2,973		$	4,711		$	4,172
Claims recovery	—			3,158			—
Franchise taxes	(11		)	(172		)	(144		)
Other	189			4			158
Other income, net	$	3,151		$	7,701		$	4,186

Cash Flow Information

Non-cash Operating Activity

The Predecessor settled $9,315 and $7,506 of its total interest expense incurred on long-term debt payable to Westlake as an addition to principal on debt outstanding in 2014 and 2013, respectively.

Non-cash Investing Activity

The change in capital expenditure accrual reducing additions to property, plant and equipment was $418, $7,937 and $1,333 for the years ended December 31, 2014, 2013 and 2012, respectively.

Non-cash Financing Activity

Related party notes payable to Westlake of $238,600 were deemed settled through net investment in 2013. The non-cash settlement was recorded as an increase in Westlake's net investment in the Predecessor. No cash was transferred in connection with the deemed settlement of these notes.

Interest and Income Taxes

Westlake uses a centralized cash management system to finance its operations. Interest paid, net of interest capitalized, and income taxes have been paid directly by Westlake and charged to the Predecessor through related party accounts receivable, net. Related party accounts receivable, net were settled immediately through net investment, and therefore, the Predecessor did not pay cash for interest expense or income tax expense during the years ended December 31, 2013 or 2012. Interest paid, net of interest capitalized, was $1,366 for the year ended December 31, 2014.

15. Major Customer and Concentration of Credit Risk

During the years ended December 31, 2014, 2013 and 2012, Westlake accounted for approximately 73.8%, 75.3% and 67.0%, respectively, of OpCo's and the Predecessor's net sales.

16. Commitments and Contingencies

OpCo is subject to environmental laws and regulations that can impose civil and criminal sanctions and that may require it to mitigate the effects of contamination caused by the release or disposal of hazardous substances into the environment. These laws include the federal Clean Air Act, the federal Water Pollution Control Act, the Resource Conservation and Recovery Act ("RCRA"), the Comprehensive Environmental Response, Compensation, and Liability Act ("CERCLA"), the Toxic Substances Control Act and various other federal, state and local laws and regulations. Under CERCLA, an owner or operator of property may be held strictly liable for remediating contamination without regard to whether that person caused the contamination, and without regard to whether the practices that resulted in the contamination were legal at the time they occurred. Because OpCo's production sites have a history of industrial use, it is impossible to predict precisely what effect these legal requirements will have on OpCo. Westlake will indemnify OpCo for liabilities that occurred or existed prior to August 4, 2014.

Contract Disputes with Goodrich and PolyOne. In connection with the 1990 and 1997 acquisitions of the Goodrich Corporation ("Goodrich") chemical manufacturing facility in Calvert City, Kentucky, which is a portion of the B.F. Goodrich superfund site, Goodrich agreed to indemnify Westlake for any liabilities related to preexisting contamination at the site.

24

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

Westlake agreed to indemnify Goodrich for post-closing contamination caused by Westlake's operations. The soil and groundwater at the site had been extensively contaminated under Goodrich's operations. In 1993, Goodrich spun off the predecessor of PolyOne Corporation ("PolyOne"), and that the Predecessor assumed Goodrich's indemnification obligations relating to preexisting contamination.

In 2003, litigation arose among Westlake, Goodrich and PolyOne with respect to the allocation of the cost of remediating contamination at the site. The parties settled this litigation in December 2007, and the case was dismissed. In the settlement the parties agreed that, among other things: (1) PolyOne would pay 100% of the costs (with specified exceptions), net of recoveries or credits from third parties, incurred with respect to environmental issues at the Calvert City site from August 1, 2007 forward; (2) either Westlake or PolyOne might, from time to time in the future (but not more than once every five years), institute an arbitration proceeding to adjust that percentage; and (3) Westlake and PolyOne would negotiate a new environmental remediation utilities and services and secondment agreement to cover Westlake's provision to or on behalf of PolyOne of certain environmental remediation services at the site. The current environmental remediation activities at the Calvert City site do not have a specified termination date but are expected to last for the foreseeable future. The costs incurred by Westlake that have been invoiced to PolyOne to provide the environmental remediation services were $2,805 and $3,284 in 2014 and 2013, respectively. By letter dated March 16, 2010, PolyOne notified Westlake that it was initiating an arbitration proceeding under the settlement agreement. In this proceeding, PolyOne seeks to readjust the percentage allocation of costs and to recover approximately $1,400 from Westlake in reimbursement of previously paid remediation costs. The arbitration is currently stayed pending the outcome of discussions between other parties and their insurance carriers.

State Administrative Proceedings. There are several administrative proceedings in Kentucky involving Westlake, Goodrich and PolyOne related to the same manufacturing site in Calvert City, which includes OpCo's ethylene production facility in Calvert City. In 2003, the Kentucky Environmental and Public Protection Cabinet (the "Cabinet") re-issued Goodrich's RCRA permit which requires Goodrich to remediate contamination at the Calvert City manufacturing site. Both Goodrich and PolyOne challenged various terms of the permit in an attempt to shift Goodrich's clean-up obligations under the permit to Westlake. Westlake intervened in the proceedings. The Cabinet has suspended all corrective action under the RCRA permit in deference to a remedial investigation and feasibility study ("RIFS") being conducted, under the auspices of the U.S. Environmental Protection Agency ("EPA") pursuant to an Administrative Settlement Agreement ("AOC"), which became effective on December 9, 2009. See "Federal Administrative Proceedings" below. Periodic status conferences will be held to evaluate whether additional proceedings will be required.

Federal Administrative Proceedings. In May 2009, the Cabinet sent a letter to the EPA requesting the EPA's assistance in addressing contamination at the Calvert City site under CERCLA. In its response to the Cabinet, the EPA stated that it concurred with the Cabinet's request and would incorporate work previously conducted under the Cabinet's RCRA authority into the EPA's cleanup efforts under CERCLA. Since 1983, the EPA has been addressing contamination at an abandoned landfill adjacent to OpCo's plant which had been operated by Goodrich and which was being remediated pursuant to CERCLA. The EPA has directed Goodrich and PolyOne to conduct additional investigation activities at the landfill and at the Calvert City site. In June 2009, the EPA notified Westlake that Westlake may have potential liability under section 107(a) of CERCLA at its plant site. Liability under section 107(a) of CERCLA is strict and joint and several. The EPA also identified Goodrich and PolyOne, among others, as potentially responsible parties at the plant site. Westlake negotiated, in conjunction with the other potentially responsible parties, an AOC and an order to conduct an RIFS. Due to OpCo's ownership and current operation of the property, OpCo may be subject to additional requirements and liabilities under CERCLA.

Potential Flare Modifications. For several years, the EPA has been conducting an enforcement initiative against petroleum refineries and petrochemical plants with respect to emissions from flares. A number of companies have entered into consent agreements with the EPA requiring both modifications to reduce flare emissions and the installation of additional equipment to better track flare operations and emissions. On April 21, 2014, Westlake received a Clean Air Act Section 114 Information Request from the EPA which sought information regarding flares at the Calvert City and Lake Charles facilities. Westlake submitted information pursuant to such request, including information regarding three flares that OpCo owns. The EPA has informed Westlake that the information provided leads the EPA to believe that some of the flares are out of compliance with applicable standards. The EPA has demanded that Westlake conduct additional flare sampling and provide supplemental information. Westlake is currently in negotiations with the EPA regarding these demands, some of which are applicable to OpCo's flares. The EPA has indicated that it is seeking a consent decree with that would obligate Westlake to take corrective actions relating to the alleged noncompliance. Westlake has not agreed that any flares are out of compliance or that any corrective actions are warranted. Depending on the outcome of Westlake's negotiations with the EPA, additional controls on emissions from OpCo's flares may be required and these could result in increased capital and operating costs.

25

WESTLAKE CHEMICAL OPCO LP

NOTES TO COMBINED FINANCIAL STATEMENTS—(Continued)

(in thousands of dollars)

Louisiana Notice of Violations. The Louisiana Department of Environmental Quality ("LDEQ") has issued notices of violations ("NOVs") regarding OpCo's assets, and those of Westlake, for various air compliance issues. OpCo and Westlake are working with LDEQ to settle these claims, and a global settlement of all claims is being discussed. While settlement may result in a total civil penalty in excess of $100, such a settlement will likely cover assets owned by OpCo and Westlake, and to the extent it covers OpCo's assets, Westlake will indemnify OpCo for liabilities to the extent such liabilities occurred or existed prior to August 4, 2014.

In addition to the matters described above, OpCo is involved in various legal proceedings incidental to the conduct of its business. OpCo does not believe that any of these legal proceedings will have a material adverse effect on its financial condition, results of operations or cash flows.

Other Commitments

OpCo is obligated under various long-term and short-term noncancelable operating leases, primarily related to rail car leases and land. Several of the leases provide for renewal terms. At December 31, 2014, future minimum lease commitments were as follows:

2015	$	1,041
2016	604
2017	443
2018	127
2019	59
Thereafter	98
	$	2,372

Rental expense was approximately $3,558, $3,933 and $2,999 for the years ended December 31, 2014, 2013 and 2012, respectively.

OpCo has various purchase commitments for its capital projects and for materials, supplies and services incident to the ordinary conduct of business. Such commitments are at prices not in excess of market prices.

17. Subsequent Events

Distribution

On January 30, 2015, the Board of Directors of the general partner of OpCo declared a quarterly distribution for the quarter ended December 31, 2014 of $95,364, in total, that was paid on February 20, 2015 to the interest holders.

General

Subsequent events were evaluated through the date on which the financial statements were issued.

26