The amount of heteroatomic (NSO) compounds in the commercial blend of West Siberian oils that arrives at the Kirishi refinery has been determined by gas chromatography-mass spectrometry. Ten representative samples of oils differing in the total sulfur content were examined. To isolate NSO compounds from oil, the alkali extraction and solid-phase extraction procedures were used. The NSO concentration in the alkali extracts was semiquantitatively determined with the use of propanethiol as an internal standard. The alkali and solid-phase extracts obtained from the oil fractions with bp below 350A degrees C were found to contain 48 identifiable NSO compounds. Of these, aliphatic C(6)-C(8) alcohols (mainly secondary and tertiary) and ketones have been isolated. The concentrations of 28 mercaptans and phenols in the oil were estimated.