Exhibit 5.1

May 29, 2019

Marathon Oil Corporation5555 San Felipe StreetHouston, Texas 77056

Re: Marathon Oil Corporation Registration Statement on Form S-8

Ladies and Gentlemen:

We have served as counsel to Marathon Oil Corporation, a Delaware corporation (the “Company”) in connection with the preparation and filing with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”), of a Registration Statement on Form S-8 (the “Registration Statement”) relating to registration under the Securities Act of up to 27,900,000 shares (the “Shares”) of common stock, par value $1.00 per share (“Common Stock”), of the Company issuable in connection with the Marathon Oil Corporation 2019 Incentive Compensation Plan (the “Plan”).

We have participated in the preparation of the Registration Statement and

have reviewed the originals or copies certified or otherwise identified to our satisfaction of all

such corporate records of the Company and such other instruments and other certificates of

public officials, officers and representatives of the Company and such other persons, and we

have made such investigations of law, as we have deemed appropriate as a basis for the opinion

expressed below. 

In rendering the opinion expressed below, we have assumed the authenticity of all

documents submitted to us as originals and the conformity to the originals of all documents submitted to us as copies. In addition, we have assumed and have not verified the accuracy as to factual matters of each document we have reviewed.

Based on the foregoing, and subject to the further assumptions and qualifications set forth below, it is our opinion that the Shares have been duly authorized byall necessary corporate action of the Company and, when issued in accordance with the terms of the Plan, will be validly issued, fully paid and nonassessable.

The foregoing opinion is limited to the General Corporation Law of the State of Delaware.

We hereby consent to the use of this opinion as a part (Exhibit 5.1) of the Registration Statement. In giving such consent, we do not thereby admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act or the Rules and Regulations of the Commission thereunder. The opinion expressed herein is rendered on and as of the date hereof, and we assume no obligation to advise you, or to make any investigations, as to any legal developments or factual matters arising subsequent to the date hereof that might affect the opinion expressed herein.

Very truly yours,

CLEARY GOTTLIEB STEEN & HAMILTON LLP

By: /s/ Arthur H. Kohn_______________Arthur H. Kohn, a Partner