The biomarker composition of eight samples of Western Siberia Paleozoic oils collected from deposits dated to the Pudinskii megaswell, the Nyurol'ka depression, their junction zone, and the Krasnoleninskii dome has been studied. Several indicators of oil composition have been identified, whose value varies depending on the geological structure that accommodates the oilfield. These differences may be evidence for different local environments of the formation of petroleum hydrocarbons. According to data on the composition of aromatic hydrocarbons, the original organic matter (OM) of all the test oils was deposited in a marine environment, and the OM of the Nyurol'ka through and the junction zone accumulated in the photic zone euxinia, as evidenced by the presence of aryl isoprenoids. Data on the composition of saturated hydrocarbons suggest brackish, littoral, suboxidizing sedimentary environment and marine algae as the main biological producer.