The performance of different membrane reactors for the epoxidation of ethylene was compared with that of a conventional fixed-bed reactor (FBR), under identical overall reaction conditions, using a cesium-doped silver catalyst supported on rx-alumina. Two packed-bed membrane reactor configurations were used, one using oxygen as permeate with ethylene flowing over the catalyst bed (PBMR-O), and the other using ethylene as permeate with oxygen Rowing over the catalyst bed (PBMR-E). The study of the FBR showed that high oxygen/ethylene ratio increases ethylene oxide selectivity. The behavior of the membrane reactor was different depending on the configuration, with the PBMR-O exhibiting smaller and the PBMR-E larger ethylene oxide selectivity, as compared to the FBR. While maintaining the overall reaction conditions fixed, ethylene oxide production in the membrane reactor could be increased further by manipulating the residence time of the reactants over the catalyst bed, and the maximun value was obtained for the largest possible residence time. The results demonstrate the operational flexibility and potential attractiveness of membrane reactors, since local reactant concentrations and residence times can be tuned to optimize reactor performance.