The oxidation of carbon monoxide to form carbon dioxide and the oxidation of hydrogen to form water are the reactions of environmental and industrial importance. These two reactions have been studied independently by Monte Carlo computer simulation using Langmuir-Hinshelwood mechanism but no effort has been made to study the combined CO-H-2-O-2 reaction on these lines. Keeping in view the importance of this 3-component system, the surface coverages and production rates are studied as a function of CO partial pressure for different ratios of H-2 and O-2. The diffusion of reacting species on the surface as well as their desorption from the surface is also introduced to include temperature effects. The phase diagrams of the system are drawn to observe the behavior of these atoms/molecules on the surface and the production of CO2 and H2O are determined at different concentrations of H-2. The results are compared with 2-component systems. (C) 2009 Elsevier B.V. All rights reserved.