In a stirred gradientless reactor(6))) containing a Polish commercial RANG-19 Ni catalyst (i) 50-1200 ppm CO, or (ii) 100-5200 ppm CO2, or (iii) 50-3500 ppm CO+CO2, was methanated with a synthesis (75:25 v/v) H-2-N-2 gas at 2.5 MPa and 210-310degreesC. At reactor outlet, CO, CO2 and CH4 concentrations were measured with a Philips PU-4500 gas chromatograph (+/-5 ppmv). Before methanation, the catalyst in the reactor was reduced with H-2 at up to 400degreesC and stabilized for 6 h. In case iii, the rate of methanation of CO, which was twice of CO2, was not affected by CO2 concentration; whereas that of CO2 fell as the CO concentration was raised (effect allowed for by exponential term in eqn. (2)). To methanate CO2, catalyst activity is of crucial importance. In eqn. (2), a=1 and similar to0. 7 at CO < 500 ppm and at CO > 500 ppm, resp., and rate constants k(co) and k(co2) and exponent b must be regressed on data of Figs. 1-5.