Where present, lateral block faulting controls oil accumulation both structurally and stratigraphically. Its recognition and proper interpretation therefore are very important in oil exploration. In order to stimulate studies of major faults for possibly greater lateral offsets affecting oil exploration, outline geological maps on an imaginary but typical California Tertiary basin are used in a "controlled experiment." Interpretations of typical, actual, structural, and stratigraphic situations by mainly vertical movements are contrasted with their very different interpretations by mainly lateral offsets in a strain relief system. These identical situations in both interpretations show that where such a system exists, as in California, the proper interpretation will aid greatly in locating traps and reservoirs for oil.