Study of the adsorption of gases on metal surface has gained renewed importance in the last decade due to the advent sophisticated surface technique. CO oxidation on metal surface is one of the most important catalytic reactions due primarily to two reasons. Technologically, it is a very important reaction in car-exhaust emission control, CO lasers, air purification and sensors. Scientifically, it is one of the simplest catalytic reactions and thus is widely used as a model system to understand heterogeneous catalysis.