Thermal transformations of petroleum components of paraffin-base heavy crude oil and oils (hydrocarbon concentrate), a mixture of oils and resins (maltenes), and a mixture of oils with asphaltenes isolated from the crude have been studied in order to assess the effect of resins and asphaltenes on the hydrocarbon conversion direction. Thermolysis of samples has been conducted at 450A degrees C for 2 h in the isothermal mode. Data on the material balance of the process have been obtained, and the composition of the gaseous and liquid products of thermolysis has been determined. The gaseous products of thermolysis consist of hydrogen, carbon dioxide, and C-1-C-5 hydrocarbons. It has been shown that the thermolysis of all the samples is accompanied by the appearance of newly formed resins and asphaltenes. Analysis of the dynamics of changes in the hydrocarbon composition of the liquid thermolysis products has shown that the resins, rather than asphaltenes affect to a greater extent the direction of hydrocarbon cracking reactions.