The hydrolysis of olive oil catalyzed by Candida rugosa lipase in sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane and the synthetic sodium bis(2-ethylhexyl polyoxyethylene)sulfosuccinate (MAOT)/isooctane reverse micellar systems was investigated in a polysulfone hollow fiber membrane reactor with recycle of the reaction mixture. Lipase was completely retained by the membrane while olive oil and oleic acid freely passed through. The retention of reverse micelles depended on W-0 (molar ratio of water to surfactant). At an olive oil concentration of 0.23 mol l(-1) the final substrate conversion in the MAOT micellar system was about 1.4 times of that in the AOT micellar system.