This study presents numerical studies of hydrogen production performance via water gas shift reaction in membrane reactor. The pre-exponential factor in describing the hydrogen permeation flux is used as the main parameter to account for the membrane permeance variation. The operating pressure, temperature and H2O/CO molar ratio are chosen in the 1-20 atm, 400-600 degrees C and 1-3 ranges, respectively. Based on the numerical simulation results three distinct CO conversion regimes exist based on the pre-exponential factor value. For low pre-exponential factors corresponding to low membrane permeance, the CO conversion approaches to that obtained from a conventional reactor without hydrogen removal. For high pre-exponential factor, high CO conversion and H-2 recovery with constant values can be obtained. For intermediate pre-exponential factor range both CO conversion and H-2 recovery vary linearly with the pre-exponential factor. In the high membrane permeation case CO conversion and H-2 recovery approach limiting values as the operating pressure increases. Increasing the H2O/CO molar ratio results in an increase in CO conversion but decrease in H-2 recovery due to hydrogen permeation driving force reduction. As the feed rate increases in the reaction side both the CO conversion and hydrogen recovery decrease because of decreased reactant residence time. The sweep gas flow rate has a significant effect on hydrogen recovery. Low sweep gas flow rate results in low CO conversion H-2 recovery while limiting CO conversion and hydrogen recovery can be reached for the high membrane permeance and high sweep gas flow rate cases. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.