The reaction O+CO->CO2 on platinum is the limiting stage of heterogeneous oxidization of carbon monoxide. The rate constant of this reaction was evaluated using the transition state theory. In this case, the reaction activation energy should be lower than the diffusion activation energy. The the results of calculations of the rate constant is presented in the figure along with the available experimental data. It is seen that the transition state theory with the parameters obtained from quantum chemical calculations provides a quantitative description of the direct bimolecular reaction.