Marathon Petroleum Corporation is a United States based petroleum refining, marketing, and transportation company. The company was formed as a subsidiary on September 1, 2005, from the former Marathon Ashland Petroleum, LLC, and is based in Findlay, Ohio.Marathon Petroleum operated as a subsidiary of the Marathon Oil Corporation until becoming a standalone company on July 1, 2011.he company was formed as a subsidiary on September 1, 2005, from the former Marathon Ashland Petroleum, LLC, and is based in Findlay, Ohio. Marathon Petroleum operated as a subsidiary of the Marathon Oil Corporation until becoming a standalone company on July 1, 2011.