Geological and geochemical data on the composition of crude oils and condensates from Aptian-Cenomanian sediments of the northern regions of Western Siberia have been summarized and systematized in order to identify the characteristics of hydrocarbon fluids generated by weakly transformed organic matter of terrigenic carbonaceous lithofacies. It has been shown that these sediments are characterized by a peculiar form of condensate and crude oil. The absence of n-alkanes and the distribution of cyclic hydrocarbons (mono-, bi-, tri-, and tetracyclanes) distinguish these accumulations represented by chemical types B-1 and B-2. The presence of biomarkers, their composition, and values of their ratios in the oils suggest the early (immature) evolution stage of oil generation. Immature Western Siberia crude oils form a single nickel type of fluid (V/Ni < 1). Their significant differences in trace element composition from the oils generated by a more transformed organic matter have been revealed.