Filed by: Marathon Oil Corporation

Pursuant to Rule 425 under the

Securities Act of 1933

and deemed filed pursuant to Rule 14a-12

under the Securities Exchange Act of 1934

Subject Company: Marathon Oil Corporation

Commission File No.: 001-05153

On May 29, 2024, the Chief Executive Officer of Marathon Oil Corporation sent the following email to its employees.

Dear MRO One Team,

Earlier this morning, we announced that MRO and ConocoPhillips have entered into an agreement pursuant to which MRO will be acquired by ConocoPhillips in an all-stock transaction. More details about the terms of this agreement can be found in the Press Release [link].

I want to express my deepest gratitude to each one of you for your unwavering loyalty, dedication and hard work. Your efforts and collective contributions have been instrumental in building a remarkable company and played a significant role in making MRO such a valued and sought-after company.

This acquisition marks the next chapter in our incredible journey and will allow the combined company to benefit from increased durability, scale and long-term sustainability.

Over our company’s rich 130-year history, we’ve always been guided by our values to make the right long-term decisions for our stakeholders. We see an outstanding strategic and cultural fit with ConocoPhillips and are confident that bringing our companies together is the right decision for the future.

That said, we’re mindful of the impact this announcement has on you, your families and your future and the uncertainty it creates. We know that there will be many questions about this transaction, particularly about how this impacts your employment.

We aim to ensure that this transaction is respectful of the contributions of our employees, either by offering the opportunity to join the newly combined organization or by providing severance packages. Some employees may be offered full-time or transition positions at ConocoPhillips. Employees will also have the chance to apply for other open roles at ConocoPhillips.

You’ll receive an invitation to an All Employee Town Hall this morning at 10:30 a.m. on the 6^th floor in Houston or via MS Teams so that we can provide additional information. A calendar invitation will follow this message.

There will also be an investor call hosted by ConocoPhillips just prior to the town hall at 9:00 a.m., the details of which are linked here. Finally, we’ve also established a dedicated sharepoint site [link] as our communications hub. This site will go live immediately after you receive this message and will include detailed answers to Frequently Asked Questions.

In the coming weeks, we’ll share more information about the transition process as details are finalized in collaboration with both management teams. We’re committed to keeping you informed throughout the process, with respect for our employees and transparent and timely updates our top priorities.

On behalf of the Board and our leadership team, I want to thank you again for your hard work, dedication and commitment to our company, which has led us to this transformative transaction.

While we understand that this is a big announcement to absorb, we know that in the days and weeks ahead that you will continue operating our business safely and responsibly with the same pride and diligence that have brought us to where we are today.

Lee

Forward-Looking Statements

This communication includes “forward-looking statements” as defined under the federal securities laws. All statements other than statements of historical fact included or incorporated by reference in this communication, including, among other things, statements regarding the proposed business combination transaction between ConocoPhillips (“ConocoPhillips”) and Marathon Oil Corporation (“Marathon”), future events, plans and anticipated results of operations, business strategies, the anticipated benefits of the proposed transaction, the anticipated impact of the proposed transaction on the combined company’s business and future financial and operating results, the expected amount and timing of synergies from the proposed transaction, the anticipated closing date for the proposed transaction and other aspects of ConocoPhillips’ or Marathon’s operations or operating results are forward-looking statements. Words and phrases such as “ambition,” “anticipate,” “estimate,” “believe,” “budget,” “continue,” “could,” “intend,” “may,” “plan,” “potential,” “predict,” “seek,” “should,” “will,” “would,” “expect,” “objective,” “projection,” “forecast,” “goal,” “guidance,” “outlook,” “effort,” “target” and other similar words can be used to identify forward-looking statements. However, the absence of these words does not mean that the statements are not forward-looking. Where, in any forward-looking statement, ConocoPhillips or Marathon expresses an expectation or belief as to future results, such expectation or belief is expressed in good faith and believed to be reasonable at the time such forward-looking statement is made. However, these statements are not guarantees of future performance and involve certain risks, uncertainties and other factors beyond ConocoPhillips’ or Marathon’s control. Therefore, actual outcomes and results may differ materially from what is expressed or forecast in the forward-looking statements.

The following important factors and uncertainties, among others, could cause actual results or events to differ materially from those described in forward-looking statements: ConocoPhillips’ ability to successfully integrate Marathon’s businesses and technologies, which may result in the combined company not operating as effectively and efficiently as expected; the risk that the expected benefits and synergies of the proposed transaction may not be fully achieved in a timely manner, or at all; the risk that ConocoPhillips or Marathon will be unable to retain and hire key personnel and maintain relationships with their suppliers and customers; the risk associated with Marathon’s ability to obtain the approval of its stockholders required to consummate the proposed transaction and the timing of the closing of the proposed transaction, including the risk that the conditions to the transaction are not satisfied on a timely basis or at all or the failure of the transaction to close for any other reason or to close on the anticipated terms, including the anticipated tax treatment; the risk that any regulatory approval, consent or authorization that may be required for the proposed transaction is not obtained or is obtained subject to conditions that are not anticipated; the occurrence of any event, change or other circumstance that could give rise to the termination of the proposed transaction; unanticipated difficulties, liabilities or expenditures relating to the transaction; the effect of the announcement, pendency or completion of the proposed transaction on the parties’ business relationships and business operations generally; the effect of the announcement or pendency of the proposed transaction on the parties’ common stock prices and uncertainty as to the long-term value of ConocoPhillips’ or Marathon’s common stock; risks that the proposed transaction disrupts current plans and operations of ConocoPhillips or Marathon and their respective management teams and potential difficulties in hiring or retaining employees as a result of the proposed transaction; and other economic business competitive and/or regulatory factors affecting ConocoPhillips’ or Marathon’s businesses generally as set forth in their filings with the Securities and Exchange Commission (the “SEC”). The registration statement on Form S-4 and proxy statement/prospectus that will be filed with the SEC will describe additional risks in connection with the proposed transaction. While the list of factors presented here is, and the list of factors to be presented in the registration statement on Form S-4 and proxy statement/prospectus are considered representative, no such list should

be considered to be a complete statement of all potential risks and uncertainties. For additional information about other factors that could cause actual results to differ materially from those described in the forward-looking statements, please refer to ConocoPhillips’ and Marathon’s respective periodic reports and other filings with the SEC, including the risk factors contained in ConocoPhillips’ and Marathon’s most recent Quarterly Reports on Form 10-Q and Annual Reports on Form 10-K. Forward-looking statements represent current expectations and are inherently uncertain and are made only as of the date hereof (or, if applicable, the dates indicated in such statement). Except as required by law, neither ConocoPhillips nor Marathon undertakes or assumes any obligation to update any forward-looking statements, whether as a result of new information or to reflect subsequent events or circumstances or otherwise.

No Offer or Solicitation

This communication is not intended to and shall not constitute an offer to buy or sell or the solicitation of an offer to buy or sell any securities, or a solicitation of any vote or approval, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offering of securities shall be made, except by means of a prospectus meeting the requirements of Section 10 of the U.S. Securities Act of 1933, as amended.

Additional Information about the Merger and Where to Find It

In connection with the proposed transaction, ConocoPhillips intends to file with the SEC a registration statement on Form S-4, which will include a proxy statement of Marathon that also constitutes a prospectus of ConocoPhillips common shares to be offered in the proposed transaction. Each of ConocoPhillips and Marathon may also file other relevant documents with the SEC regarding the proposed transaction. This communication is not a substitute for the proxy statement/prospectus or registration statement or any other document that ConocoPhillips or Marathon may file with the SEC. The definitive proxy statement/prospectus (if and when available) will be mailed to stockholders of Marathon. INVESTORS AND SECURITY HOLDERS ARE URGED TO READ THE REGISTRATION STATEMENT, PROXY STATEMENT/PROSPECTUS AND ANY OTHER RELEVANT DOCUMENTS THAT MAY BE FILED WITH THE SEC, AS WELL AS ANY AMENDMENTS OR SUPPLEMENTS TO THESE DOCUMENTS, CAREFULLY AND IN THEIR ENTIRETY IF AND WHEN THEY BECOME AVAILABLE BECAUSE THEY CONTAIN OR WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED TRANSACTION. Investors and security holders will be able to obtain free copies of the registration statement and proxy statement/prospectus (if and when available) and other documents containing important information about ConocoPhillips, Marathon and the proposed transaction, once such documents are filed with the SEC through the website maintained by the SEC at www.sec.gov. Copies of the documents filed with the SEC by ConocoPhillips will be available free of charge on ConocoPhillips’ website at www.conocophillips.com or by contacting ConocoPhillips’ Investor Relations Department by email at investor.relations@conocophillips.com or by phone at 281-293-5000. Copies of the documents filed with the SEC by Marathon will be available free of charge on Marathon’s website at https://ir.marathonoil.com/ or by contacting Marathon at 713-629-6600.

Participants in the Solicitation

ConocoPhillips, Marathon and certain of their respective directors and executive officers may be deemed to be participants in the solicitation of proxies in respect of the proposed transaction. Information about the directors and executive officers of ConocoPhillips is set forth in (i) ConocoPhillips’ proxy statement for its 2024 annual meeting of stockholders under the headings “Executive Compensation”, “Item 1: Election of Directors and Director Biographies” (including “Related Party Transactions” and “Director Compensation”), “Compensation Discussion and Analysis”, “Executive Compensation Tables” and “Stock Ownership”, which was filed with the SEC on April 1, 2024 and is available at

https://www.sec.gov/ix?doc=/Archives/edgar/data/1163165/000130817924000384/cop4258041-def14a.htm, (ii) ConocoPhillips’ Annual Report on Form 10-K for the fiscal year ended December 31, 2023, including under the headings “Item 10. Directors, Executive Officers and Corporate Governance”, “Item 11. Executive Compensation”, “Item 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters” and “Item 13.

Certain Relationships and Related Transactions, and Director Independence”, which was filed with the SEC on February 15, 2024 and is available at https://www.sec.gov/ix?doc=/Archives/edgar/data/1163165/000116316524000010/cop-20231231.htm and (iii) to the extent holdings of ConocoPhillips securities by its directors or executive officers have changed since the amounts set forth in ConocoPhillips’ proxy statement for its 2024 annual meeting of stockholders, such changes have been or will be reflected on Initial Statement of Beneficial Ownership of Securities on Form 3, Statement of Changes in Beneficial Ownership on Form 4 or Annual Statement of Changes in Beneficial Ownership of Securities on Form 5, filed with the SEC (which are available at EDGAR Search Results https://www.sec.gov/edgar/search/#/category=form-cat2&ciks=0001163165&entityName=CONOCOPHILLIPS%2520(COP)%2520(CIK%25200001163165)). Information about the directors and executive officers of Marathon is set forth in (i) Marathon’s proxy statement for its 2024 annual meeting of stockholders under the headings “Proposal 1: Election of Directors”, “Director Compensation”, “Security Ownership of Certain Beneficial Owners and Management”, “Compensation Discussion and Analysis”, “Executive Compensation” and “Transactions with Related Persons”, which was filed with the SEC on April 10, 2024 and is available at https://www.sec.gov/ix?doc=/Archives/edgar/data/0000101778/000010177824000082/mro-20240405.htm, (ii) Marathon’s Annual Report on Form 10-K for the fiscal year ended December 31, 2023, including under the headings “Item 10. Directors, Executive Officers and Corporate Governance”, “Item 11. Executive Compensation”, “Item 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters” and “Item 13. Certain Relationships and Related Transactions, and Director Independence”, which was filed with the SEC on February 22, 2024 and is available at https://www.sec.gov/ix?doc=/Archives/edgar/data/0000101778/000010177824000023/mro-20231231.htm and (iii) to the extent holdings of Marathon securities by its directors or executive officers have changed since the amounts set forth in Marathon’s proxy statement for its 2024 annual meeting of stockholders, such changes have been or will be reflected on Initial Statement of Beneficial Ownership of Securities on Form 3, Statement of Changes in Beneficial Ownership on Form 4, or Annual Statement of Changes in Beneficial Ownership of Securities on Form 5, filed with the SEC (which are available at EDGAR Search Results https://www.sec.gov/edgar/search/#/category=form-cat2&ciks=0000101778&entityName=MARATHON%2520OIL%2520CORP%2520(MRO)%2520(CIK%25200000101778)).

Other information regarding the participants in the proxy solicitations and a description of their direct and indirect interests, by security holdings or otherwise, will be contained in the proxy statement/prospectus and other relevant materials to be filed with the SEC regarding the proposed transaction when such materials become available. Investors should read the proxy statement/prospectus carefully when it becomes available before making any voting or investment decisions. Copies of the documents filed with the SEC by ConocoPhillips and Marathon will be available free of charge through the website maintained by the SEC at www.sec.gov. Additionally, copies of documents filed with the SEC by ConocoPhillips will be available free of charge on ConocoPhillips’ website at www.conocophillips.com/ and those filed by Marathon will be available free of charge on Marathon’s website at https://ir.marathonoil.com/.