Crude oils and shale from the northern Denver basin were analyzed using organic geochemical techniques to determine oil-source-bed relations. Geochemical analyses show that, in general, Cretaceous oils are compositionally similar throughout the basin and are dissimilar to oil produced from the Permian Lyons Sandstone.

Shales were evaluated for source-rock potential based on quantity of contained organic matter, thermal maturity, and geochemical correlation with crude oils. These analyses showed that most of the Cretaceous oils have been derived from the Carlile Shale, Greenhorn Limestone, Graneros Shale, and Mowry Shale interval. These units have a maximum collective thickness of about 500 ft (152 m) and can be grouped together on the basis of similar geochemistry. The source bed for the Lyons oil has not been identified.

Regional geochemical study of the Carlile-Greenhorn-Graneros-Mowry interval shows that effective source beds are limited to the basin-axis area. Although shale samples from eastern Colorado and southwestern Nebraska are rich in organic matter, they are generally thermally immature. The presence of petroleum on the east flank of the basin and the limited geographic distribution of effective source beds indicate that extensive (perhaps 100 mi or 160 km) lateral migration has occurred.

Cretaceous oils in reservoirs in the Terry and Hygiene Sandstone Members of the Pierre Shale have probably undergone extensive vertical migration (about 2,500 ft or 762 m in the central Front Range area).