[7] After the U.S. Supreme Court ordered its parent company to break up as a result of the Sherman Anti-Trust Act in 1911, Ohio Oil again became independent.

[11] MPC also owns the general partner and majority limited partner interest in MPLX LP, a midstream company which owns and operates gathering, processing, and fractionation assets, as well as crude oil and light product transportation and logistics infrastructure.

In 2006, it adopted its current slogan, "Fueling the American Spirit" as the company shifts emphasis on work ethic and the contributions of its employees.

[13] In 2005, the company became a 100% owned subsidiary of Marathon Oil, after Ashland sold off its downstream assets and exited the retail business.

[15] In 2009, the company completed a $3.9 billion expansion of its refinery in Garyville, Louisiana, that increased the plant's capacity by 180,000 barrels per day.

[14] In 2010, the company sold its 74,000 barrel-per-day refinery in St. Paul Park, Minnesota, along with associated terminals, pipelines, and inventory as well as 166 SuperAmerica convenience stores to Northern Tier Energy for $900 million.

[19] In 2014, Speedway LLC, a now-former subsidiary of the company, purchased the retail operations of Hess Corporation for $2.82 billion.

[20] The deal also introduced the Marathon brand name at stations for the first time in the Northeastern United States east of the Appalachian Mountains and north of Pennsylvania.

Prior to the deal, Marathon's traditional marketing territory for decades had been the Midwestern and Southeastern United States, never going further east than the Pittsburgh metropolitan area.

[24] After some time, residents and some local schools were evacuated due to the poorer air quality as precaution, but the response was not immediate.

[25][23][24] On April 30, 2018, Marathon agreed to buy Andeavor, an independent refinery and oil company based in the Western United States, for $23 billion.