<p>Sequential hydrous pyrolysis was applied to an organic-rich source-rock sample from the Upper Devonian Domanik Formation of the Timan-Pechora Basin to investigate changes in hydrocarbon biomarkers during experimental maturation. The Domanik Formation is a major source-rock interval within the Domanik-Paleozoic petroleum system and is composed of organic-rich carbonate-siliceous deposits with predominantly type II kerogen and high petroleum-generative potential. The study compares the initial oil and source-rock extractable organic matter with generated liquid products and residual extracts obtained after three successive hydrous-pyrolysis stages at 300&#xa0;°C for 72&#xa0;h under closed-system conditions. The results show that repeated hydrous pyrolysis causes systematic changes in <i>n</i>-alkane, isoprenoid, sterane, and terpane parameters. Several commonly used correlation and maturity indices remain comparable between the initial oil and source-rock extract, but diverge markedly after successive pyrolysis stages. These observations indicate that sequential hydrous pyrolysis modifies biomarker signatures through continued generation, cracking, and redistribution of soluble organic products. Therefore, biomarker-based oil–oil and source rock–oil correlations should be interpreted cautiously when laboratory-generated products or strongly transformed fluids are compared directly. The observed increase in the C₂₈/C₂₉ sterane ratio during successive stages may reflect selective transformation of sterane precursors, but this interpretation remains a working hypothesis that requires further testing on additional samples. The study demonstrates the usefulness of sequential hydrous pyrolysis for tracing biomarker redistribution during maturation.</p>