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In order to evaluate the adsorption and catalytic effects of indigenous carbonates and silicates on the organic matter of Aleksinac oil shale, the free and the bound bitumens were isolated and analyzed by organic geochemical methods. The differences in the gross compositions indicated an adsorption effect of both the carbonates and silicates in the examined oil shale. The maturation parameters, based on n-alkanes and isoprenoid alkanes pristane and phytane, indicated that bitumen 3 was of the highest, and bitumen 1 of the lowest, apparent maturity. The silicates were shown to have had a thermocatalytic effect on the organic matter of this sediment. Clay minerals had a catalytic effect primarily on sterane aromatization, rearrangement of steranes into diasteranes and their (20R) → (20S) isomerization. All evidence obtained by analysis of steranes and aromatic steroids suggested that the differences in bitumen compositions should be explained by the effect of clay minerals rather than by variations in the origin of the precursor biomass. © 1992.