Abstract <p>The effect of hydrogen donors, tetralin and 1-propanol, and of the Ni–Fe catalyst in combination with 1-propanol on the thermal degradation of the organic matter of the carbonate–siliceous rock from the Romashkino field with 7.07% C_org content in supercritical water at 374°С and pressures from 18 to 24 MPa was revealed. 1-Propanol, compared to tetralin, influences the kerogen degradation in supercritical water more efficiently and suppresses the coking. The degradation of alkyl chains of the organic matter to form saturated hydrocarbons occurs in the presence of 1-propanol most intensely. Introduction of 1-propanol into the reaction system in combination with the Ni–Fe catalyst initiates the kerogen degradation to liquid petroleum fractions to a lesser extent but activates the condensation leading to the formation of large amounts of carbenes/carboids and coke. Depending on introduction of various additives into the reaction system, the most significant differences are observed in the structural-group composition of resins in which the ratio of the СН₃/СН₂ groups decreases and the content of oxygen-containing S=O, С=О, and О–Н groups increases as the extent of condensation of their structure decreases. In contrast to resins, the degree of aromaticity and degree of condensation of asphaltenes increase owing to an increase in the number of hydrogen atoms in the structure of the rings. A common trend for asphaltenes and resins in all the experiments is an increase in the content of hydroxyl О–Н groups. The carbenes/carboids are characterized by relatively low content of aliphatic CH₂ and CH₃ groups and oxygen-containing СО groups and by high degrees of aromaticity and condensation of their structure.</p>