Proton-transport-membrane water gas shift (WGS) reactors, based on thin dense SrCe0.7Zr0.2Eu0.1O3-delta membranes on tubular Ni-SrCe0.8Zr0.2O3-delta supports, were developed to increase H-2 yields relative to thermodynamic limitations. Pure H-2 permeate, total H-2 production, and reactor side CO conversion and H-2/CO effluent ratio were measured as a function of temperature, flow rate, CO concentration and H2O/CO feed ratios. CO conversion, total H-2 production and yield, and the H-2/CO in the reactor side effluent increased with increasing temperature and H2O/CO feed ratios. CO conversions of 84% and 90% were achieved at 900 degrees C with H2O/CO feed ratios of 1/1 and 2/1, respectively. These respective 77% and 44% increases in CO conversion compared to feed gas condition thermodynamics resulted in 73% and 42% increases in H-2 production. Permeated H-2 and total H-2 production increased with increasing flow rate and CO concentration. Finally, membrane stability under WGS conditions was significantly improved by Zr substitution. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.