Today, many of the industry's critical problems result from an oversupply of relatively cheap oil because, on a worldwide basis, recent exploration has been too successful. California has had a glorious role in this petroleum exploration for a period of nearly 100 years. During most of this time it has ranked as the first or second oil-producing state. Furthermore, it has been a substantial foreign exporter of crude oil and products. The state's production history is characterized by substantial annual increases up through 1953, and an annual decline since that year. The annual discovered reserves during this same period, however, show great fluctuations; since 1940 the annual discovered reserves have been relatively small and much below annual production. The principal oil-producing areas of California are the San Joaquin, Los Angeles, Ventura, Santa Maria, and Cuyama-Salinas basins. To the end of 1961, the 295 oil fields in the state have produced about 12.3 billion barrels of crude. The changing exploration methods are illustrated by the discovery of 6 selected oil fields. The Midway-Sunset field was discovered in 1901 by drilling near oil seeps. The Ventura Avenue oil field discovery in 1916 marked the early application of surface geology and the anticlinal theory. The Santa Fe Springs field in 1919 is important as the first discovery attributed to the geomorphologic concept of domal structure being reflected in alluviated surface topography. The 1936 Wilmington field discovery was the result of the early use of the seismic reflection method. This field is also famous as the world's largest water-flooding operation. The Russell Ranch field discovered in 1948 exemplifies the combination of surface and subsurface geology. The Wheeler Ridge oil field discovered in 1922 in shallow Miocene sands was rediscovered in 1952 in Eocene sands below a subsurface thrust fault, an example of success by subsurface geology and deeper drilling. Present oil exploration is high in state offshore areas partly because of new techniques for drilling and completing wells in water. All petroleum geologists are challenged to find petroleum reserves at competitive costs, to contribute to the science of geology and its applications, to advance the professional competence of geologists, and to contribute to the economic prosperity of our states and our nation.