Tosco was an independent US based petroleum refining and marketing corporation. It was founded in 1955 and grew to become the largest independent oil refining and fuel marketer in the United States during the 1990s, with more than 5,000 Circle K, Union 76, BP, Exxon, and Shell convenience store and service stations. Tosco merged with Phillips Petroleum in 2001. Phillips merged with Conoco in 2002 to become ConocoPhillips, who spun off the Circle K stores to Canadian-based Alimentation Couche-Tard.