The influence of various media on the degree of transformation of kerogen of Domanikovian rocks in hydrothermal processes was studied in model experiments. Autoclave experiments were conducted with debituminized rock in inert, hydrogen, and carbon dioxide media. A common mechanism was observed for all the reaction media under the influence of hydrothermal factors: the kerogen content in the rocks decreases and the yield of free hydrocarbons extractable from the rocks by organic solvents increases. The saturated hydrocarbon content is higher in the group composition of the experiment products compared to the original extract due to decrease in resin and aromatic hydrocarbon content. In the original extract from the Domanikovian rock, as well as in the experiment products, there are two solid dispersed phases, namely, asphaltenes soluble in aromatic solvents and their modified structures of the type of carbenes and carboids insoluble in toluene due to their more condensed structure with a smaller number of aliphatic substituents. The most pronounced decrease in resin content is observed in carbon dioxide medium with a marked increase in asphaltene content in the experiment products relative to the original extract. In hydrogen medium, on the other hand, asphaltene content decreases in the experiment products, but, in comparison with the carbon dioxide medium, carbenes and carboids are formed more intensely due to decomposition of the kerogen structure. Asphaltenes and carbenes-carboids were found to differ in structure and paramagnetic properties.