The effects of oxygen supply conditions and specific biofilm interfacial area on the phenol removal rate in a three-phase fluidized bed bioreactor were evaluated. the experimental data were well-explained by the semi-theoretical equation based on the assumption that the reaction rate follows first-order reaction kinetics with respect to oxygen and zero-order one with respect to phenol. Two cases; biological reaction as rate-controlling step and oxygen absorption as rate-controlling step, were both explicable by this semi-theoretical equation. The maximum volumetric phenol removal rate was 27.4 kg.m(-3) d(-1).