Simulated results are presented using a reaction rate equation and a one-dimensional reactor model for a water gas shift reaction (WGSR) in a membrane reactor (MR) with a feed stream obtained from coal gasifiers. CO conversion in a MR at 423-573 K was higher than equilibrium conversion at the same temperature. The effect of two important parameters of a membrane, hydrogen selectivity and hydrogen permeance, on MR performance was studied and hydrogen selectivity was favorable for enhanced CO conversion, reduced CO concentration, and enhanced fuel-cell grade hydrogen. Hydrogen permeance was also favorable for CO conversion enhancement in a MR due to an increased driving force between the shell side (retentate) and the tube side (permeate) of a membrane. The criteria of a hydrogen permeance of higher than 8×10.8 mol m.2s.1Pa.1 and a hydrogen selectivity of 100 were suggested to produce a fuel-cell grade hydrogen (CO concentration less than 50 ppm) in the permeate and a concentrated CO2 (more than 90%) in the retentate simultaneously in a MR.