Offshore oil and gas in California provides a significant portion of the state's petroleum production. Offshore oil and gas has been a contentious issue for decades, first over the question of state versus federal ownership, but since 1969 mostly over questions of resource development versus environmental protection. Notable offshore fields include the Ellwood Oil Field and the Wilmington Oil Field, both of which are partially onshore and partially offshore, and the large Dos Cuadras Field in the Santa Barbara Channel, which is entirely in the federal zone.