Biological removal of organic sulfur from petroleum feedstocks offers an attractive alternative to conventional thermochemical treatment due to the mild operating conditions afforded by the biocatalyst, In order for biodesulfurization to realize commercial success, it will be necessary to design reactors that allow for sufficient liquid/liquid and gas/liquid mass transfer while simultaneously reducing operating costs. In this study, the use of electric field contactors for the biodesulfurization of the model compound dibenzothiophene (DBT) as well as actual crude oil was investigated. The emulsion phase contactor (EPC) creates an emulsion of aqueous biocatalyst in the organic phase by concentrating forces at the liquid/liquid interface rather than by imparting energy to the bulk solution as is done in impeller-based reactors. Characterization of emulsion quality and determination of rates of DBT oxidation to 2-hydroxybiphenyl (2-HBP) were performed for both batch stirred reactors (BSR) and the EPC. The EPC was capable of producing aqueous droplets of about 5 mu m in diameter using 3 W/1 whereas the impeller-based reactor formed droplets between 100 and 200 mu m with comparable power consumption, The presence of electric fields was not found to adversely affect biocatalytic activity. Despite the greater surface area for reaction afforded by the EPC, rates of DBT oxidation in both reactors were similar, demonstrating that the biocatalyst used (Rhodococcus sp. IGTS8) was not active enough to be mass transport limited, The EPC is expected to have tremendous impact on reactor operating costs and biocatalyst utilization once advances in biocatalyst development provide systems that are mass transport limited.