Sunoco 's an American petroleum and petrochemical manufacturer headquartered in Philadelphia, Pennsylvania, United States, formerly known as Sun Company Inc. (1886-1920 and 1976-1998) and Sun Oil Co. (1920-1976). In Canada, Sunoco's operated by Suncor Energy, a separate Canadian entity. Sunoco's a Fortune 100 Company. It's also the biggest company based in Philadelphia and the 2nd biggest in Pennsylvania behind AmerisourceBergen. History 1800s to 1900s: founding and growth The integrated oil co… (More on Sunoco)