Abstract The structural-group composition and the properties of organosulfur compounds of oil fraction of Bavly petroleum are studied. We show that organosulfur compounds are predominantly (64.7%) made up of sulfides. The mass spectroscopic data indicate that the sulfides of the oil fraction contain mainly the saturated compounds in the absence of aromatic sulfides. The organosulfur compounds of the oil fraction, whose empirical formula is CnH2n–4S, contain 35.3% of the thiophene derivatives, among which alkylthiophenes are prevalent with their share ranging from 64 to 80%. Thiaindanes having the formula CnH2n–6S are ranked in second place in terms of content (ranging from 15 to 21%).