The spatial and temporal distribution of petroleum-degrading bacteria(PDB) was studied at six sampling sites in Kyeonggi Bay of the Yellow Sea fiom March 1990 to October 1991. In addition, petroleum-degrading potcntial of natural ~iiai-ineb acterial population was studied at different culturc contlitions. During the period o f stutly. thc heterotrophic bacterial number and PDB number were n1e;rsured in the range of 7 000-108.400 CFU/nil. 0-2.800 MPN1100 mi. respectively. The spatial tlistribution of PDB wa highly affected by presence of petroleum hydrocarbon. In laboratory cxperirncnt. petrolcu~n biodegradation wac enhanced hy addition of yeast cxtracl. cell free cxtr:~ct. anti rnixctl culture of PI)B.