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Progress in solving the secrets of the origin and accumu- lation of petroleum took a giant step forward in 1859 with the drilling of the first oil well. This initial well was drilled to a depth of 69 feet. Oil and gas deposits had been encoun- tered at various locations since ancient times, but these in- stances were relatively rare in 1859. Today we have widely accepted geologic theories along with good supporting evidence that help explain how oil and gas were formed. Once formed in the sedimentary source beds, the oil and gas then migrated to other sedimentary rocks where we find them today. This two-step sequence is the starting place for this introduction.

Life on earth possibly began hundreds of millions of years ago in vast seas and inland lakes. This is one of the initial concepts in developing the current geologic organic theory of petroleum. These marine areas are thought of as being reasonably shallow. The hydrogen and carbon material which makes up the composition of petroleum is presumed to have come from the decomposed plants and animals that were living on land and in the sea. It is probable that the greatest contribution of organic matenal was deposited in a marine environment rather than a continental environment. Also, it is believed that the small plant and animal forms were of more importance than the larger forms as a petro- leum source.