Abstract: In order to increase the oil degradation rate of the two strains of petroleum degrading bacteria,DH-5 and DH-9 isolated from the soil of the Shengli Oilfield,tests were done to screen out optimal composition of the medium for theri growth and environmental conditions for petroleum degradation.It was found that Strain DH-5 gres the bese when the medium was composed of 1 g·L^-1 crude oil,400 mg·L^-1 N sources,200 mg·L^-1 P sources,20 mg·L^-1 yeast extract,and 10 mg·L^-1 arginine(Arg),which was the most effective among acid,and it performed the best when it was in an environment being 7.0 in pH,20 in salinity and 15-30℃ in temperature.And under such conditions,oil degradation rate of DH-5 in creased 11.57 percent point.For best growth,DH-9 should be cultured in the medium composed of 1 g·L^-1 crude oil,400 mg·L^-1 N sources,100 mg·L^-1 P sources,20 mg·L^-1 yeast extract,and 10 mg·L^-1 aspartic acid (Asp) which was the most effective among amino acid,and it did the best in an environment being 7.5 in pH,20 in salinity and 30℃ in temperature.Under such conditions,Strain DH-9 could degrade 64.10% of crude oil,oil degradation rate increasing 20.88 percent point.When the oil concentration reached 20 g·L^-1 ,DH-9 was 158% and 129% higher than DH-5 inbiomass and oil degradation rate,respectively.The findings indicate that Strain DH-9 is significantly more tolerant to high concentrations of credu oil than Strain DH-5,but Strain DH-5 is more adaptable to low temperature than Stratin DH-9.Besides,both of the two strains show strong adaptability to higy salinity,which characterizes the local environment.