The kinetics of the transesterification of soybean oil has been investigated in a centrifugal contactor reactor/separator at temperatures from 45 to 80 degrees C and pressures up to 2.6 bar. The high shear force and turbulent mixing achieved in the contactor minimized the effect of diffusion on the apparent reaction rate, and hence it could be assumed that the transesterification rate was limited by the reaction kinetics. The yields of product methyl esters were quantified using gas chromatography flame ionization detection (GC-FID), infrared (IR) spectroscopy, proton nuclear magnetic resonance ((HNMR)-N-1), and viscosity measurements and typically were found to achieve 90% of complete conversion within 2 min. However, to meet American Society for Testing and Materials (ASTM) specifications with one pass through the reactor, a minimum 22-min residence time at 80 degrees C was needed. Performance was improved by stepwise processing, allowing separation of byproduct glycerine and injection of additional small aliquots of methanol at each step. The chemical kinetics was successfully modeled using a three-step mechanism of reversible reactions, and employing activation energies from the literature, with some modification in pre-exponential factors. The mechanism correctly predicted the exponential decline in reaction rate as increasing methyl ester and glycerine concentrations allow reverse reactions to occur at significant rates.