California is one of the prolific oil and gas producing provinces of the United States. To date 12,350,000,000 barrels of oil and 17,122,000,000 MCF of gas have been produced. Estimated oil reserves are 3,550,000,000 barrels and estimated gas reserves 8,822,000,000 MCF.

The six important oil-producing sedimentary basins with estimated ultimate proved production are: (1) San Joaquin, 7,270,000,000 barrels; (2) Los Angeles, 6,070,000,000 barrels; (3) Ventura, 1,919,000,000 barrels; (4) Santa Maria, 684,000,000 barrels; (5) Cuyama, 375,000,000 barrels; (6) Salinas, 225,000,000 barrels. The most important dry gas producing basin, the Sacramento, has an estimated ultimate recovery of 4,800,000,000 MCF.

These basins are aligned in a general northwest-southeast trend paralleling the mountain systems of California. The San Joaquin basin with 10,000 square miles is the largest and the Los Angeles basin with 700 square miles is the smallest. The east-west-trending Ventura basin lays claim to being the narrowest and yet the deepest with approximately 60,000 feet of sediments in the synclinal trough. The sedimentary section in these basins ranges from Upper Cretaceous through Quaternary. Intensive folding, thrust faulting, and abrupt facies changes are common. Most of the oil fields are anticlinal and are characterized by high productivity per acre. Sandstones are the predominant reservoirs with Miocene (48%) and Pliocene (41.6%) accounting for most of California's oil.

California's first commercial oil field was discovered in 1898. The peak discovery years were the twenties when a plethora of new fields flooded the market and resulted in the first curtailment program. The advent of the seismograph in the thirties was followed by major discoveries. During the last 20 years, with the exception of 1948 and 1949, it has been a struggle to maintain reserves. Economic factors, including the increased cost of drilling to deeper objectives, higher royalties and land costs, expanding suburban development and the flood of foreign imports have become deterrents to many operators.

Despite this somewhat darkening picture there remain substantial parts of California's sedimentary basins that have not been adequately prospected and which should contain profitable oil and (or) gas accumulations. Provided with the opportunity, imaginative and aggressive geologists can keep California in the "prolific producing" category.

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