Sixty samples, selected from a 2,300-foot core of the Green River Formation in Colorado, were studied to ascertain differences in the structure of the organic material present in the oil shale samples. Emphasis was placed upon relating differences in the aromatic content of the insoluble kerogen and the alkane content of the extractable material obtained from the selected samples. The methods used in determining these differences consisted of fractionation of the soluble material, carbon and hydrogen analysis, volatile material determination, carbon residue determination, oxidation rate determination, and infrared analysis. In general it was concluded that the organic material in this core does vary in chemical structure and that some of these variations resulted from factors related to depth of burial. Other observed changes in structure of the organic material were not depth dependent and resulted from other factors such as source material variations, biological alterations, or ecological differences. Work done in cooperation with the University of Wyoming.