A bioenergetic model has been developed to estimate cometabolism coefficient along with mainte-nance coefficient for cometabolism process where small amounts of toxic materials exist with major carbon and energy source(eg. glucose) in the waste water. Cometabolism coefficient and maximum bioenergetic yield were estimated as 0.1026(1/h)and 0.585, respectively for the growth of Pseudomonas sp. under aerobic continuous cultivation. It also turned out that phenol was utilized as a cometabolic substrate where its concentration was below 20㎍/ml. Pre-cul-tivation with a phenol analog, m-cresol enhanced biodegradation rates of phenol and also increased total biomass concentration along with the extension of stationary phase.