The Lompoc Oil Field is a large oil field in the Purisima Hills north of Lompoc, California, in Santa Barbara County. Discovered in 1903, two years after the discovery of the Orcutt Oil Field in the Solomon Hills, it is one of the oldest oil fields in northern Santa Barbara County, and one of the closest to exhaustion, reporting only 1.7 million barrels (270,000 m3) of recoverable oil remaining out of its original 50 million barrels (7,900,000 m3) as of the end of 2008. Its sole operator is Sentinel Peak Resources, who acquired it from Freeport-McMoRan. In 2009, the proposed decommissioning and habitat restoration of the 3,700-acre (15 km2) field was part of a controversial and so-far unsuccessful deal between Plains, several environmental groups, Santa Barbara County, and the State of California, to allow Plains to carry out new offshore oil drilling on the Tranquillon Ridge, in the Pacific Ocean about twenty miles (32 km) southwest of the Lompoc field.

The Monterey Formation is an extensive Miocene oil-rich geological sedimentary formation in California, with outcrops of the formation in parts of the California Coast Ranges, Peninsular Ranges, and on some of California's off-shore islands. The type locality is near the city of Monterey, California. The Monterey Formation is the major source-rock for 37 to 38 billion barrels of oil in conventional traps such as sandstones. This is most of California's known oil resources. The Monterey has been extensively investigated and mapped for petroleum potential, and is of major importance for understanding the complex geological history of California. Its rocks are mostly highly siliceous strata that vary greatly in composition, stratigraphy, and tectono-stratigraphic history.