High Quality Content by WIKIPEDIA articles! The Ventura Oil Field is a large and currently productive oil field in the hills immediately north of the city of Ventura in southern California in the United States. It is bisected by California State Route 33, the freeway connecting Ventura to Ojai, and is about eight miles (13 km) long by two across, with the long axis aligned east to west. Discovered in 1919, and with a cumulative production of just under a billion barrels of oil as of 2008, it is the seventh-largest oil field in California, retaining approximately 50 million barrels in reserve, and had 423 wells still producing. As of 2009 it was entirely operated by Aera Energy LLC.