Organic matter extracted from Green River oil shale by supercritical extraction experiments was characterized by elemental analysis, number average molecular weight determination and field ionization mass spectrometry. The organic matter was also separated into fractions of organic acids, bases, and hydrocarbons. Characterization data demonstrate that the organic matter recovered in high yield from autoclave experiments is similar in composition to organic matter extracted in low yield at solvent reflux temperatures. The composition of organic matter extracted from Green River shale by supercritical techniques is compared with the composition of Green River shale oil produced by several pilot-scale retorting processes.