The microbial community in the area of oil seep in Mid-Baikal (Cape Gorevoi Utes) was studied. The number of microorganisms that oxidize normal hydrocarbons, petroleum, and easily accessible organic matter in the water mass of the lake, bottom sediments, and bitumen structures was studied in 2005-2009. The high heterogeneity of the distribution of microorganisms associated with the deparaffination of oil in the areas of oil seeps was noted. The maximum concentrations of hydrocarbon-oxidizing microorganisms in the samples of bottom water above bitumen structures (up to 2200 +/- 175 CFU/ml) and in bitumen structures themselves (up to 170000 +/- 13000 CFU/g) were determined. A model experiment showed that in the conditions of low temperatures (4 degrees C) the degradation of the fraction of oil n-alkanes by the natural microbial community reaches 90% over a period of 60 days.