2020, This study is devoted to conversion of heavy oil in sandstone, taken from the Ashalchinskoye field in Tatarstan, Russian Federation, in the presence of an oil-soluble catalyst precursor based on a transition metal of iron in water vapor. The mass content of a portion of the catalyst, in a hydrogen donor based solution totals 2.0 wt % of the oil extract in the rock sample. It was found that according to the results of the chemical composition study, the introduction of the catalyst ensures the conversion of resins (by 24 wt %) at 250?C and a significant conversion of asphaltenes at 300?C, the content of which decreases practically to «trace« amounts at this temperature. The intensification of the destructive processes of breaking heteroatom bonds in the molecules of resins and asphaltenes contributes to the generation of light liquid hydrocarbons. ? 2020 IOP Publishing Ltd. All rights reserved.