This study investigated the bio-treatability of PCB contaminated oil for the development of design and operational parameters for the bioreactor. Input of external carbon and nutrient source in the aqueous phase was found to be required for the treatment of polychlorinated biphenyls (PCBs)-contaminated oil. Addition of surfactant was investigated for the emulsification of oil to reduce interference of contact with microorganisms and PCBs. The ratio of surfactant to oil was empirically optimized to 1 : 1. The higher PCB removal efficiency was obtained at 30 days of hydraulic retention time (HRT) in the semi-batch reactor study without cell recycle. The removal efficiency measured in mixed liquor was maintained at over 85% on average at 32 +/- 2 degrees C and 30% at 22 +/- 2 degrees C. More than 0.2 g/l/d of the organic loading rate was suggested to be maintained for various PCB loading rates (0.02-0.6 mg-PCB/l/d). For high biomass retaining and easy collection of treated oil, an Anaerobic Sequencing Batch Reactor (ASBR) was investigated. The removal of Aroclor was observed as more than 50% in the oil phase with 3 days reaction time and about 40% in overall phases, i.e. oil, liquid, biomass phases at 22 +/- 2 degrees C. US EPA verification results on the process performance are included in this presentation.