The kinetics of reaction of carbon monoxide and carbon dioxide with hydrogen in a nickel catalyst tube wall reactor were investigated experimentally and the reaction mechanisms were clarified. The observed rate laws were -rco = (k1PH2P1/2CO)/(1 + KCOPCO) for carbon monoxide, and -rco2 = (k''PH2P1/3CO2)/(1 + KCO2PCO2 + KH2 + KH2OPH2O)for carbon dioxide at low partial pressure. These reaction rate laws were derived theoretically from the proposed reaction mechanism. For a mixture of carbon monoxide and carbon dioxide the kinetics of the reaction proved to be well accounted for by the same reaction mechanism.