The water gas shift (WGS) reaction was examined over Pt and Pt-CeOx catalysts supported on CexZr1-xO2 (Ce0.06Zr0.95O2, Ce0.2Zr0.8O2, Ce0.4Zr0.6O2, Ce0.6Zr0.4O2, Ce0.7Zr0.3O2 and Ce0.8Zr0.2O2) under severe reaction conditions, viz. 6.7 mol% CO, 6.7 mol% CO2, and 33.2 mol % H2O in H-2. The catalysts were characterized with several techniques, including X-ray diffraction (XRD), CO chemisorption, temperature-programmed reduction (TPR) with H-2, temperature-programmed oxidation (TPO), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and bright-field transmission electron microscopy (TEM). Among the supported Pt catalysts tested, Pt/Ce0.4Zr0.6O2 showed the highest WGS activity in all temperature ranges. An improvement in the WGS activity was observed when CeOx was added with Pt on CexZr1-xO2 supports (x = 0.05 and 0.2) due to intimate contact between Pt and CeOx species. Based on CO chemisorptions and TPR profiles, it has been found that the interaction between Pt species and surface ceria-zirconia species is beneficial to the WGS reaction. A gradual decrease in the catalytic activity with time-on-stream was found over Pt and Pt CeOx catalysts supported on CexZr1-xO2, which can be explained by a decrease in the Pt dispersion. The participation of surface carbonate species on deactivation appeared to be minor because no improvement in the catalytic activity was found after the regeneration step where the aged catalyst was calcined in 10 mol% O-2 in He at 773 K and subsequently reduced in H-2 at 673 K. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.