A comparison of the composition of crude oils from six zones ranging in age from Jurassic to Cretaceous in the Tow Creek, Wilson Creek, Iles, and Moffat fields, and oil from a seep at Tow Creek, Colorado, shows that, except at Wilson Creek, the oil in each pool is unlike the oil in all other pools of these fields, whether at the same or a different stratigraphic position. In the Wilson Creek field the oil from the Sundance formation is similar to the oil from the overlying Morrison formation. These facts may indicate that, except at Wilson Creek, the source of the oil of each pool was local to that pool; or the data may indicate that the oil of the several pools was at one time similar and was affected differently during the folding and faulting that formed the domes and nticlines. The oil in the Morrison formation at Wilson Creek may have migrated upward from the Sundance formation. The oil in the north Tow Creek pool and the oil in the seep at Tow Creek may have been altered by an intrusive body that occupies a large area in the north part of the Tow Creek anticline. On the other hand, the differences between the oils near the intrusive body are no greater than between oils in a region in Oklahoma containing no intrusive bodies, which has been investigated recently by the research committee of the Tulsa Geological Society.

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