Modified MFI-type zeolite membranes were investigated as high-temperature water-gas shift (WGS) membrane reactors (MRs) in combination with a nanocrystalline Fe/Ce WGS catalyst. The effects of the MR operating conditions and the membrane separation performance on the CO conversion (chi(CO)) were studied experimentally and by calculations using a simple one-dimensional plug-flow reactor (PFR) model. The experimental results showed that, at high temperatures (e.g., >500 degrees C), the zeolite MR with moderate H-2 selectivity (e.g., alpha(H2/CO2) similar to 31, and alpha(H2/CO) similar to 25) and permeance (P-m,P-H2 similar to 0.9 x 10(-7) mol s(-1) m(-2) Pa-1) was capable of overcoming the limit of equilibrium CO conversion and chi(CO) of the MR could be further enhanced by increasing the reaction pressure while keeping the permeate pressure unchanged. At high temperatures and high reaction pressures, CO is rapidly consumed by a fast reaction that minimizes the membrane permeation of unreacted CO; meanwhile, the efficiency of H-2 removal is improved as a result of the increased H-2 partial pressure difference across the membrane. The model calculations have indicated that the current membrane has the potential to achieve high CO conversion of chi(CO) > 99% under practically meaningful operating conditions.