The assessment of oil and gas resource potential of the San Joaquin Basin, California, by the U.S. Geological Survey, is discussed. Two categories of future additions to reserves were evaluated, first was resource in undiscovered accumulations and second was growth of reserves in already discovered accumulations. The mean estimate of undiscovered oil resources is 393 barrels. The greatest potential for oil accumulations larger than 10 million barrels is probably in Miocene and Eocene reservoirs of the westside of the basin and in deep basin south of the Bakersfield Arch.