In the design of water gas shift reactors, the performance of catalysts is not known a priori and hence having a general kinetic expression will be of much help. Computational Fluid Dynamic study was carried out to investigate the performance of a packed bed reactor for different feed compositions using five commonly used types of macro kinetic models. User Defined Functions were developed for the reaction rate to predict the CO conversion in the reactor. The effects of temperature and time factor on CO conversion were studied. The Langmuir-Hinshelwood model gave the best prediction for H-2 rich mixtures. The Temkin model was better for higher CO concentrations, whereas the other models gave large deviations for the fixed bed reactor. (C) 2011 Elsevier Ltd. All rights reserved.