The distributions of biomarkers (triterpanes, steranes) in the hydrocarbon fractions of the Tremembé (São Paulo), Maraú (Bahia), and Irati (Paraná) oil-shales were examined by gas chromatography-mass spectrometry. The stereochemistry of these biomarkers allowed inferences about the relative levels of maturity of the shales, with the carbon number distributions of the steranes yielding information as to lhe principal types of organic input to the sediments. The distributions of biomarkers in extracts were confirmed by examination of pyrolyzates, an approach which proved effective in ruling out the possibilíty of low level impregnation of one of the shales (Maraú) by petroleum from the sub-surface.The distributions of biomarkers (triterpanes, steranes) in the hydrocarbon fractions of the Tremembé (São Paulo), Maraú (Bahia), and Irati (Paraná) oil-shales were examined by gas chromatography-mass spectrometry. The stereochemistry of these biomarkers allowed inferences about the relative levels of maturity of the shales, with the carbon number distributions of the steranes yielding information as to lhe principal types of organic input to the sediments. The distributions of biomarkers in extracts were confirmed by examination of pyrolyzates, an approach which proved effective in ruling out the possibilíty of low level impregnation of one of the shales (Maraú) by petroleum from the sub-surface.