"Thirty-four analyses of crude oils from the fields of the Four Corners Area of Arizona, Colorado, New Mexico, and Utah are presented and compared. The samples, taken from formations in four geological time periods, have high gravity and low-sulfur, nitrogen, and asphalt content. Generally, the oils are paraffinic in the low-boiling fractions, with increasing naphthenicity in the higher-boiling fraction. Oil from Cretaceous formations resemble other Cretaceous oil in the Rocky Mountains, but oils from Permian and Pennsylvania formations are unlike other oils of these ages in the Rocky Mountains. The differences in the oils are minor and cannot be used to distinguish between fields or between producing formations. With minimum special processing, the oils should yield large amounts of good-quality motor fuels."