The kinetic modelling of the water-gas-shift (WGS) reaction in the iron-based low-temperature Fischer-Tropsch synthesis was investigated. It was found that first order kinetics in CO is a reasonable description of the CO2 formation rate, but (due to systernatic errors in this model) it appears to be essentially an empirical relationship. WGS rate expressions based on the formate mechanism were found to provide an improved description of the WGS kinetic data. By considering rate data measured over a wide range of reactor pressures, it was possible to discriminate between the various formate-based rate equations considered during this study. (c) 2007 Elsevier B.V. All rights reserved.