The West Montalvo Oil Field is a large and productive oil field on the coast of Ventura County, California, in the United States, in and adjacent to the city of Oxnard. Discovered in 1947, it has produced approximately 43.7 million barrels (6,950,000 m³) of oil, and retains about 2.2 million recoverable with current technology, in both the onshore and offshore areas. The offshore portion of the field is exploited from wells directionally drilled from onshore near McGrath Lake, from within an enclosure above the high-tide line at McGrath State Beach.