The paper deals with the main petroleum hydrocarbon sources in the earth cover. Oil products influence on intensification of different microbial forms activity as well as on bio-chemical transformation of the pollutants themselves is shown. Changes in state and properties of soils due to microbial degradation of oil products are experimentally studied. The analysis of reservoir destruction through the example of black oil fuel storage is carried out. Results of determining different groups of microorganisms in soils and groundwater in the fuel oil storage tank area cross-section are given. The role of microbial activity in bearing capacity change of sandy-argillaceous soils with specific reference is presented.