High Quality Content by WIKIPEDIA articles! The Coalinga Oil Field is a large oil field in western Fresno County, California, in the United States. It surrounds the town of Coalinga, about half-way between Los Angeles and San Francisco, to the west of Interstate 5, at the foot of the Diablo Range. Discovered in the late 19th century, it became active around 1890, and is now the eighth-largest oil field in California, with reserves totaling approximately 58 million barrels (9,200,000 m3), and over 1,600 active oil wells. The principal operators on the field, as of 2008, were Chevron Corp. (formerly Standard Oil of California or SoCal) and Aera Energy LLC.