Marathon Oil Corporation is an American petroleum and natural gas exploration and production company headquartered in the Marathon Oil Tower in Houston, Texas.

As of December 31, 2015, the company had 2.163 billion barrels of oil equivalent (1.323×10 GJ) of estimated proved reserves, of which 44% was in the United States, 32% was in Canada, 12% was in Equatorial Guinea, and 11% was in other countries in Africa, primarily Libya.

The company has concessions with the Waha Oil Company in Libya. Libya accounts for 235 million barrels of oil equivalent (1.44×10 GJ) of estimated proved reserves, although the company did not sell any product from these operations in 2015 since operations were interrupted by civil and political unrest.

In Canada, the company is focused on the Athabasca oil sands project, in which the company owns a 20% interest.

The company's proved reserves consisted 40% of petroleum, 32% synthetic crude, 19% natural gas and 9% natural gas liquids.

In 2015, the company sold 438 thousand barrels of oil equivalent (2,680,000 GJ) per day.

In 2015, the company derived 13% of its revenues from sales to Irving Oil and 11% of its revenues from sales to Shell Oil.

In 2016, the company plans to spend $1.4 billion on capital expenditures, of which $1.2 billion will be spent in North America, including $600 million in the Eagle Ford and $200 million in the Bakken formation.

The company owns 277,000 net acres in the Bakken formation.

Marathon began as The Ohio Oil Company in 1887. In 1889, it was purchased by John D. Rockefeller's Standard Oil. It remained a part of Standard Oil until Standard Oil was broken in 1911. In 1930, The Ohio Oil Company bought the Transcontinental Oil Company and established the "Marathon" brand name. In 1962, the company changed its name to "Marathon Oil Company".

In 1982, Mobil made a hostile offer to buy the company; however, the board of Marathon Oil rejected the offer and instead sold the company to United States Steel. A legal battle ensued thereafter.

After the merger, the headquarters was moved to Houston, Texas in 1990 but the company's refining subsidiary maintained its headquarters in Findlay.

In 1984, Marathon purchased the U.S. unit of Husky Energy for $505 million.

In 1998, Marathon and Ashland, Inc. contributed their refining operations to Marathon Ashland Petroleum LLC, now Marathon Petroleum.

In 2001, USX, the holding company that owned United States Steel and Marathon, spun off the steel business and, in 2002, USX renamed itself Marathon Oil Corporation.

In 2003, Marathon sold its Canadian operations to Husky Energy.

In 2003, the company sold its interest in the Yates Oil Field to Kinder Morgan for $225 million.

In late 2003, Marathon Oil and its partners Noble Energy and AMPCO started the Bioko Island Malaria Control Project (BIMCP) in Equatorial Guinea. Malaria control activities included indoor residual spraying, improved diagnosis and case management, and capacity building to contain future outbreaks. BIMCP had proven being successful in reducing malaria transmission, reducing the proportion of children with malaria parasites, and improving iron status. BIMCP is perceived as a model of hands-on corporate involvement in a humanitarian effort with government, non-profits and academic organizations to reduce the burden of malaria in countries located in Equatorial Africa. The President of Equatorial Guinea, Obiang Nguema, is one of the world's worst dictators, according to Parade Magazine. Marathon's humanitarian efforts have mitigated some of the criticism resulting from its dealings with Nguema's regime. In 2008, Marathon Oil and Lestis Group started the Central Basin Control Project (CBCP)

In 2007, Marathon purchased for approximately $6.6 billion, Marathon acquired Western Oil Sands and gained ownership of its 20 percent stake in the Athabasca Oil Sands Project in northern Alberta and other assets in the midwestern United States. The Athabasca project's Muskeg River Mine was producing 155,000 barrels a day of bitumen at the time.

In 2011, Marathon completed the corporate spin-off of Marathon Petroleum, distributing a 100% interest to its shareholders.

In June 2013, Marathon sold its Angolan oil and gas field to Sinopec for $1.52 billion.

In September 2013, Marathon announced it would sell a 10% stake in an oil and gas field offshore Angola for around $590 million to Sonangol Group.

In June 2014, Marathon Oil Norge AS (“Marathon Norway") was acquired by Det Norske Oljeselskap ASA for USD $2.1 billon.