The results of a comparative study on the composition of alkanes and metalloporphyrins found in petroleum from the weathering crust and in the organic matter dispersed in Paleozoic basement rocks and covering Jurassic deposits are reported, which allow the most likely sources of petroleum in the Pre-Jurassic basement in the southeast of West Siberia to be determined. The influence of eustatic processes on the distribution and composition of metalloporphyrins and alkanes in ancient sediments is shown.