Wyoming crude oils generally are divided by practical oil men into two groups, the "green oils" and the "black oils." The former term refers to oil which is generally green , has a low sulfur content, is rather paraffinic, and yields appreciably higher amounts of straight run gasoline. The "black oils", on the other hand, are black, have high sulfur content, are asphaltic, and yields lesser quantities of straight run gasoline. While this division is useful, additional information may be gained by further classification, especially with regard to the geologic age of the formation in which the oil is found.