Two liquid-liquid bioreactors, a stirred-tank and a novel electrostatic-dispersion system, are being used to investigate biodesulfurization of oil by sulfate-reducing bacteria (SRB). The hydrodynamic behavior of both bioreactors under various operating conditions is discussed in this article. The total liquid volume of the stirred-tank system is 1 L in a 1.5-L cylindrical tank equipped with two baffles and two Rushton-type six-blade impellers. The steady-state average drop size (d(32)) was determined by a video technique, and correlated with operating conditions, physical properties, and system geometry. Although the stirred-tank geometry was not standard, the d(32) correlation was found to be in good agreement with correlations reported in the literature. For the electrostatic dispersion system, a 0.25-L column was used with kerosene as the continuous phase and water containing SRB as the dispersed phase. Microdroplets were obtained by the break-up of the aqueous phase meniscus at the tip of a capillary tube using pulsed direct current (dc) electric fields. The size of the drops ejected from the capillary was measured as a function of the intensity of the applied voltage. Preliminary results showed no deleterious effect of electrospray dispersion on bacteria viability.