The composition of the organosulfur compounds of the oil fraction of Arlan oil was studied using a method involving the two-step oxidation of these compounds with 30% hydrogen peroxide in the presence of an acid catalyst at 80 degrees and 100 degrees C. Vacuum distillation of the organosulfur compounds into narrow fractions showed that the sulfoxides obtained by oxidation of the organic sulfur compounds of the oil fraction are thiamono-, thiabi-, and thiatricycloalkanes, aliphatic sulfides, and alkylcycloalkyl sulfides. No aromatic compounds were detected in the sulfoxides. Sulfones in the narrow fractions are mainly represented by thiaindanes, alkylcyclano- and alkylbicyclanobenzthiophenes with long alkyl substituents containing from 10 to 15 carbon atoms.