Oxide support plays a significant role in the mechanistic reaction sequence for the water-gas shift (WGS) reaction over Pt-based catalysts. In situ FTIR spectroscopic and transient kinetic studies have been used to follow the reactions that occur. CeO2-, TiO2-, and ZrO2-supported Pt catalysts have been studied at 300 degrees C. In all cases, CO is adsorbed on Pt. The role of the support oxide is to activate water, completing the WGS reaction sequence. We have taken into consideration four different pathways that may be involved in the complex WGS reaction scheme: (A) redox route, (B) associative formate route, (C) associative formate route with red-ox regeneration of the oxide support, and (D) carbonate route. In the case of Pt/ZrO2, the WGS reaction follows the associative formate route with red-ox regeneration (route C). On Pt/TiO2, both the red-ox route (A) and the associative formate route with red-ox regeneration (C) contribute. The associative formate route (B) is the relevant reaction pathway on Pt/CeO2. (c) 2007 Elsevier Inc. All rights reserved.