A study has been made of two specimens of Ashal＇chinsk natural bitumen produced by natural inflow (native) and by steam and heat treatment (SHT). Natural SHT bitumen has a lower density and viscosity and a considerably lower pour point. The reduction in these indices is due to a greater amount of light fractions on account of the degradative and mass-exchange processes that occur in the formation when natural bitumen comes into contact with steam. The medium-distillate fractions of the investigated specimens of Ashal＇chinsk natural bitumen are similar in potential content of organosulphur compounds. The smaller amount of aromatic structures in average molecules of narrow fractions obtained from natural SHT bitumen simplifies the isolation of organosulphur compounds from them. This makes it possible to give preference to natural SHT bitumen as promising feedstock for the production of organosulphur compounds.