Tesoro Corporation was an independent petroleum refining and marketing company founded in 1968 by Dr. Robert Van Osdell West Jr. The company initially focused on petroleum exploration and production, quickly expanding into refining with its first refinery near Kenai, Alaska, in 1969. Over the years, Tesoro grew through acquisitions, operating ten refineries across the Western United States, including states like California, Alaska, and Washington.

Tesoro's core business segments included refining, where it processed crude oil into products such as gasoline and diesel, achieving a refining capacity of approximately 664,000 barrels per day. The company also engaged in marketing and distribution, selling refined products in bulk and operating retail gasoline stations under various brands. Additionally, Tesoro Logistics LP managed logistics for crude oil gathering, transportation, and storage, enhancing operational efficiency. In 2018, Tesoro was acquired by Marathon Petroleum Corporation, further expanding its reach in the refining and marketing sectors.