Chromato-mass-spectrometric studies made it possible to identify a wide spectrum of hydrocarbon biomarkers in crude oils from Cenomanian pools of northern West Siberia (Russkoe, Pangodinskoe, Van-Eganskoe, Severo-Komsomol'skoe). The distribution pattern of the main hydrocarbon components (n-alkanes, acyclic isoprenanes, steranes, terpanes) shows that most of the oils underwent intense microbial oxidation. We have established high concentrations of 25-norhopanes typical of high-degree degradation; demethylated hopanes are also revealed in "alkane" crude oils. Among low-molecular chemofossils, bi- and tricyclic mono and sesquiterpanes have been recognized, whose precursors are usually biomolecules synthesized by plants. Unsaturated precursors of mono and sesquiterpanes might have been the starting material for thermocatalytical synthesis of framework adamantanoid structures, whose high concentrations have been found in alkane-free crude oils
