The occurrence of bacteria living in the surface water of various lakes, rivers and in soil and their capability to degrade various motor-oils was studied. The development dynamics of microorganisms degrading crude oil derivatives in various seasons of the year and their generic composition was determined. It has been found that the highest numbers of motor-oil degrading bacteria occurred in environments polluted with those substances (soil in the area of a petrol station and from the road-side). The largest number of bacteria capable of utilizing motor-oil was found in autumn, the smallest in winter. Among the motor-oils studied (diesel oil, Selectol Special, Lotos Semisyntetic, Selenia Synthetic), the most easily assimilable by microorganisms was diesel oil, and the least - Lotos Semisyntetic.