The process of aerobic enzymatic biodegradation of oil recovered from the Khanty-Mansiysk oilfield was carried out in the liquid medium. In the process of biodegradation changes in the physicochemical properties of oil and its component composition have been determined. IR spectrometric analyses of the oil samples biodegraded for 30 and 60 days showed different degradation levels in the compositions of hydrocarbon functional groups. The compositions of individual alkanes in the oil were studied using gas-liquid chromatography (GLC). The data obtained enabled to calculate the biomarker values including the coefficient of biodegradation depending on the time of the oil contact with hydrocarbon-oxidizing microflora. The oil samples with different degrees of biodegradation were studied in the process of hydrates and ice formations using exothermic and endothermic reactions. The probability of gas hydrate nucleation in the degraded oils was found to be higher than that in the crude oil.