Transformation mechanisms of the mobile-hydrocarbon composition of rock samples from the Domanik deposits of the Volga-Ural oil-and-gas-bearing province (OGP) are established. IR spectra of extracts obtained from the rock and of resins and asphaltenes after heat treatment are analyzed. The aromaticity of the asphaltenes increases to a maximum at 250A degrees C due to degradation of aliphatic substituents and condensation of aromatic rings under radical-recombination conditions. This correlates with group-analysis results indicating that the maximum asphaltene content is observed at this temperature. Transformation of the mobile-hydrocarbon composition is associated with transformations of the composition and structure of the insoluble organic matter kerogen. The degree of maturity of organic matter of the Domanik deposits is characteristically low, increases steadily with increasing temperature, and reaches a maximum at 350A degrees C.