Andeavor was an independent petroleum refining and marketing company founded in 1968, originally known as Tesoro Corporation. Headquartered in San Antonio, Texas, it transitioned to focus primarily on refining and marketing petroleum products by the late 1990s. In 2017, the company was renamed Andeavor to reflect its growth into a premier refining, marketing, and logistics entity. It operated 10 refineries in the Western United States, with a combined crude oil refining capacity of approximately 1.1 to 1.2 million barrels per day.

Andeavor managed a retail network of around 3,000 branded gas stations, including well-known brands like Tesoro, Shell, and ExxonMobil. The company also provided midstream logistics services through Andeavor Logistics LP, which included transportation, terminalling, and wholesale fuel distribution. With significant revenues and a large workforce, Andeavor was recognized as a Fortune 100 company before its acquisition by Marathon Petroleum in 2018, forming the largest U.S. refiner by capacity.