Oil, tar, and natural gas have been seeping into the Santa Barbara Channel at least since the latest low sea level mark, approximately 20,000 years ago, at the height of the last ice age. At that time, many of the oil-bearing formations were exposed to erosion at the earth's surface, around the edge of the Santa Barbara - Ventura geologic basin. Today, those erosional surfaces are still exposed or covered with a thin layer of sedimentation. Thousands of those seeps are active all over the basin, some now covered by rising sea level (about 350-400 feet in the last 20,000 years).
You can still hear the aged, hippy, eco-Nazis and their Hollywood socialist collaborators complain about the leaking oil production platforms. But the fact of the matter is, the operations in the Santa Barbara Channel have been the cleanest and safest in the world since 1969 (when the regulations were changed after the oil spill there). The natural seepage (on the order of 100-150 barrels per day) dwarfs the level of accidental spillage. The oil in runoff from the streets of Los Angeles after a heavy rain dwarfs the natural level of seepage for the same time period.