Degradation of Baku oil, refinery products (diesel fuel, kerosene, and gasoline), and some individual aromatic hydrocarbons (toluene, p-xylene, and ethylbenzene) by micromycete cultures isolated from Caspian Sea water and coastal soil near the Apsheron peninsula was studied. The intensity of biodegradation of crude oil and petroleum products with micromycetes was determined by measuring carbon dioxide evolution and biomass formation. The conditions for chromatographic analyses of biodegradation products were determined. The dynamics of structure and composition of the test petrochemicals during oxidation with micromycetes was studied by means of gas-liquid and gas-solid chromatography and IR and H-1 NMR spectroscopy. It was found that, under cooxidizing conditions, microorganisms convert toluene and p-xylene into the corresponding monocarboxylic acids and acetophenone (35-40%) and phenylacetic acid (60-65%) are formed in the case of ethylbenzene.