The most resistant to the effects of microorganisms and other environmental factors among the components of oil are PAHs because of toxic exposure and insolubility in water. On one hand, the insolubility in water reduces the probability or prevents the ingress of PAH in living organisms; on the other hand, it leads to their accumulation in the environment, for example in the bottom sediments of reservoirs. The influence of light and ionizing radiation, pH, mineral water environment, presence of humic acids in soil, etc. affect their transformation in the environment. The research results of transformation of PAH during petroleum degradation in soil of Surakhani oil field of Absheron have been presented in the paper. The analyses were performed on the device GC/MS Trace DSQ (Thermo Electron, Finngan USA, 2005) within the range of m/z =35-400 (m/z-mass to charge ratio), and the components in the products were identified on the base of mass-spectra. Because the polycyclic compounds are the most toxic from the ecological point of view, the study of their changes during oil degradation processes in the environment is of interest. The individual PAHs (especially benzo- compounds) exceeds others’ toxicity a thousand times. Therefore, the mutual transformations of these PAHs are reasonable from the ecological point of view, and the study of these processes under different factors is of great practical and scientific interest. It should be mentioned that the presence of all three groups of PAH exceeds their values in the tar fractions of both crude and degraded in soil petroleum in comparison with the oil fractions. Thus, in the tar fraction of crude oil the content of 2-6 PAH is 45%, 16 EPA – 33,6% and NPD – 38,5% higher than in the oil fraction. We have studied the class of PAH 16 EPA in more detail. The dependence of the ratio of the concentrations of the individual PAH in tar (Ct) and oil (Co) fractions on their molecular weight and number of aromatic rings (k) is given in figure 1. The figure shows that with an increase in both of these values the Ct/Co ratio increases. Moreover, this value in the crude oil grows faster than in the degraded one, and at k > 3 this ratio becomes 2,5 times greater than in the degraded oil. In degraded oil, this ratio does not exceed 4 at all values of k. Within the oil degradation in soil the PAH content decreases both in oil and tar fractions. The decrease in 2-6 PAH rings amounts to 33,5% for oil and 49,8% - for tar fraction. The appropriate numbers for NPD are - 34,5% and 49,4%, and for 16 EPA - 48,8% and 43,2%. For all groups of PAH there is a reduction in their content within the degradation of oil in soil. This relates to the measurable PAH in the oil composition. The ratio of individual PAH content in oil and tar fractions of oil (n) strongly depends on the number of benzene rings (k), and reaches up to 13,6 at k=6 in crude oil. This dependence in degraded oil in soil gets relatively weak character, and the value n does not exceed 4 at k=5-6. Within the degradation of oil in soil the content of light PAH is strongly transformed both in the oil and tar, the content of relatively heavy PAH with k=4 – 6 changes only 1.5-2 times. Reduction in PAH content in degradation process is likely due to the destructive and polycondensation processes.