Based on data on the density and viscosity of petroleum extracts taken from the Pashian section of the Bavlinskoe oil field, on the distributions of components (lube oils, benzene- and alcohol-benzene-extractable resins, and asphaltenes), and on the hydrocarbon and structural-group compositions, it was shown that half the pore space of a reservoir of about 5 m in thickness near the oil-water contact contains bitumen with a low mobility, and the second half is filled by its condensation products. It was found that the lower part of the reservoir is the domain of the deposition of asphaltenes from the heavy petroleum that primarily filled the reservoir, as a result of mixing with arriving light oil in the course of the multistage formation of the oil field.