Biological markers, compounds derived essentially unchanged from living organisms, are found in oil-bearing rocks, petroleum and most ancient sediments. We are investigating the variation in ratios of certain biomarkers in shale oils and their use as tracers for relating oil to source rock during in-situ retorting. We have produced oil samples at heating rates of about 10/sup 0/C/min from 1- and 2-foot shale composites from three Green River formation cores and have measured the occurrence of several isoprenoid and polycycloalkane compounds in the oils using capillary gas chromatography. To eliminate the effect of heating rate on alkene/alkane ratios, we used the sum of ene and ane forms where applicable to calculate ratios. Variations in biomarker content with depth, grade, odd/even ratios, normal alkene/alkane ratios and atomic nitrogen/organic carbon ratios were studied and cross correlations were determined. Correlations were particularly high between pairs of isoprenoid compounds. There is sufficient variation to use biomarkers as retort diagnostics and to demonstrate a variation in source material.