Almost 100% CO selectivity was achieved with small pulses of CH4/O-2 (2/1), using very short residence times over a reduced NiO/La2O3 catalyst. One concludes that CH4 conversion depends on its dissociation, whereas CO selectivity is mainly dependent on the strength of oxygen binding to the catalyst. Over the reduced catalyst, the oxygen species oxidize with difficulty (because of their strong binding to metal Ni) CO to CO2, whereas over the unreduced catalyst (which contains Ni oxide), the oxygen species easily oxidize (because they are weakly adsorbed) CO to CO2.