Catalytic combustion of gasified biomass over Pt/Al2O3 was investigated to clarify its dependence on the fuel gas composition and the air-fuel ratio. An experimental study was performed using synthetic mixtures of the main components in gasified biomass : carbon monoxide, hydrogen, methane, carbon dioxide, water, benzene (model aromatic compound), ammonia, and inert (argon or nitrogen). Results showed that carbon monoxide and hydrogen ignited simultaneously over the catalyst used, with methane having a higher ignition temperature than that of carbon monoxide and hydrogen. The ignition temperature for carbon monoxide and hydrogen decreased as the oxygen-fuel ratio and inert concentration increased. The presence of water vapor in the feed had an inhibiting effect on the ignition of carbon monoxide, whereas the opposite was observed for methane. Methane ignition was favored by the presence of carbon monoxide and hydrogen, not only because their combustion heated the catalyst but also because it attenuated the oxygen inhibition of methane combustion under certain conditions. These effects were explained by co-adsorption phenomena involving fuel components and oxygen. Ammonia was found not to influence the combustion of the other components and was completely converted to nitrogen monoxide over the used catalyst.