Asphaltenes isolated from Usa crude oil have been fractionated by fractional precipitation. The bulk asphaltenes and their fractions have been subjected to thermolysis. The sulfide, thianaphthene, and aromatic sulfur content in the molecules of virgin asphaltenes and their fractions has been calculated from elemental analysis and group composition data for the thermolysis products and the results of molecular mass (MM) determination. It has been shown that the amount of the alkylsulfide functional type of sulfur depends on the MM of asphaltenes and influences on the yield of thermolysis products.