Saturated hydrocarbons from 60 selected samples of a 2,300-foot Green River Formation oil-shale core (Piceance Creek Basin, Colorado) Were analyzed by gas-liquid chromatography techniques. Emphasis was placed upon the distribution of normal alkanes and 15 key-branched and cyclic alkanes. The latter compounds consisted of the c15, c16, c18, c19, and c20 chain isoprenoids, the 5-a and 5-b c27, c28, and c29 steranes, three c30 pentacyclic triterpanes, and perhydro-b- carotene. The results showed definite evidence of maturation of both the n-alkanes and the branched and cyclic alkanes; however, most if not all of the changes were limited to the idigenous soluble extract and were not the result of additional soluble extract generation from the insoluble kerogen. Source material and environmental variations were important factors in some of the observed differences in the branched plus cyclic alkane compositions. Work done in cooperation with the University of Wyoming.