This volume presents papers that have been assembled for a Core Workshop on Miocene and Oligocene Petroleum Reservoirs of the Santa Maria and Santa Barbara - Ventura Basins, California. The main emphasis of the workshop in the Miocene Monterey Formation, the most important petroleum reservoir in both the Sana Maria Basins and a very important reservoir in the Santa Barbara - Ventura Basin, particularly in the offshore. In addition to the Monterey Formation, core studies are also presented on the post-Monterey Sisquoc Formation and on pre-Monterey reservoirs including the Sespe, Alegria, and Vaqueros Formations.