Through the study of groundwater in oilfields areas many researchers have shown that at a depth, available for drilling wells for oil exploration studies, exists diverse unique and active bacterial life. Bacterial groundwater communities are able to transform natural organic and inorganic compounds as the principal agents of the process of self-purification of groundwater. It is considered that the polluted underground waters contain the acclimatized microbial populations. At the same time essential factors for activity of the petrooxidizing bacterial community are existence in a sufficient amount of electrons acceptors and biogenous elements. The purpose of our research was the identification of places of oil penetration in underground waters around petro-development on the basis of the analysis of number of the main ecological-trophic groups of microorganisms. Determination of the cells number was performed by inoculation on solid agar nutrient media. Samples were prepared in the sterile mineral medium K1, with coefficient of dilution 10. The suspensions (0.1 ml) were plated by surface method on agar medium, corresponding to the studied ecological-trophic group. All the dilutions were plated in triplicate. Number of cells in 1 ml of the water sample was calculated using the formula M = a x 10n / V, where M – the number of cells in 1 ml, a – the average number of colonies grown after plating of this dilution, V – the volume of added suspension, ml, 10n – dilution factor. For isolation and growth of oxidizing bacteria was used agar mineral medium K1 adding oil (Zaitsev, Karasevich, 1981), for the isolation and growth of heterotrophic bacteria was used agar medium LB (Maniatis et al., 1984), for the isolation and growth of halophilic microorganisms was used agar medium Raymond (Raymond, 1961). The analysis took into account the three ecological-trophic groups of microorganisms: heterotrophic, halophilic and oil destructors. The research did not reveal the presence of halophilic microorganisms in studied water microbiocenosis. Probably, in the areas of collection of water samples are no exits of the underground brines. A significant number of heterotrophic microorganisms were mentioned in the samples №№ 18, 48, 53, 58 and 63 (2,1h from 106 to 1.4 x 107). Such level of the microorganisms of the ecological-trophic group indicates arrival of organic compounds in water samples in the sampling points. In the remaining samples the heterotrophic microorganisms are also present, but their number is close to the natural level and may be due to the presence of natural organic matter in the water. An analysis of the amount of oxidizing microorganisms suggests that in the sampling points “Well 3” and “Well 1” comes flow of petroleum hydrocarbons. The other samples showed a small amount of oil destructors, which may be part of a group of heterotrophic microorganisms, having a wide degradative capacity.