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An investigation on the effect of various microbes on degradation was carried out as part of the study on bioremediation of oil-polluted wetland at LiaoDong Bay in northeast China. The method used involved direct inoculation of selected bacteria, which were capable of degrading oil, to the soil samples. The combination of various bacteria showed better results in terms of oil degradation than any single ones due to their synergetic effects. The operation conditions [pH 8.0, 25°C, C/N/P (40:5.6:1)] for these bacteria to degrade the oil content in the soil samples were also studied and optimized. Addition of appropriate surfactants was helpful for bacteria growth, thus favoring the oil degradation. For instance, after adding Tween 80 (300 mg/kg) for 8 days, the number of bacteria was amplified 6.22 times and the rate of oil degradation increased by 20%. Adequate amount of H2O2 was also beneficial for microbes to decompose oil. However, overdosage may cause the death of the bacteria. The addition of 400 mg/l H2O2 each time was suitable. Seven thousand milligrams of H2O2 was added entirely in 11 days, and the rate of oil degradation increased significantly from 27% (without H2O2) up to 67%. The study clearly demonstrated that the direct soil inoculation was an effective method for environmental bioremediation. [ABSTRACT FROM AUTHOR]