The acetone-butanol fermentation by Clostridium acetobutylicum is receiving renewed interest as a process for large scale solvent production. The fermentation kinetics have been modeled as functions of substrate, butyrate, and butanol concentrations and pH. These models have been applied to simulate batch, single stage stirred continuous, and two stage stirred continuous fermentations. The batch simulation results accurately reproduced trends of cell growth, acid production, and solvent production reported in experimental studies. The performance of the two stage, continuous process was shown to be vastly superior to that of the single stage process on the basis of outlet butanol concentration, volumetric productivity, and substrate utilization. The ratio of the two reactor volumes which will yield the maximum productivity was found to depend upon the feed substrate concentration and the desired effluent butanol concentration. The dilution rate necessary to achieve this optimum operating state was dependent upon the ratio of the reactor volumes. / M.S.