The mineral and organic components of the core material from Vereiskian and Bashkirian deposits of the Akanskoe field in the Republic of Tatarstan have been studied by complex thermal analysis. The occurrence depth intervals with abnormally light oil have been revealed in the Bashkirian deposits. These facts together with the data on the composition of oils (high values of the ratio of light to heavy alkane homologues for heavier and more viscous Bashkirian crude oils, the bimodal MMD character of C-9-C-20 n-alkanes, and enrichment in high-molecular-mass asphaltenes at the bottom of the reservoir) suggest the influx of a lighter oil to the formed Bashkirian deposit. No facts of this sort have been identified for the Vereiskian oil.