Chemical-looping combustion is a new technology that could help reconcile the contradictory requirements of an increasing energy demand and the reduction of greenhouse gas emissions. This technique involves combustion of fossil fuels with inherent CO2 capture by means of an oxygen carrier that is circulated between air and fuel reactors. In this article, synergy effects of the combustion of methane by using a small amount of nickel oxide in a bed of iron oxide are presented. Reactivity was investigated on particles 125-180 mu m in a laboratory fluidized bed reactor of quartz. Reduction was performed in 50% CH4/50% H2O. The two oxygen carriers used are 60% NiO/40% MgAl2O4 sintered at 1400 degrees C and 60% Fe2O3/40% MgAl2O4 sintered at 1100 degrees C. It is shown that, at 950 degrees C, a bed consisting of the mixed system of 3 wt% nickel oxides with 97 wt% iron oxides produces almost two times as much carbon dioxide per time unit in comparison to the sum of carbon dioxide when the oxygen carriers were tested separately. This effect is likely due to the catalytic action of metallic Ni, which reforms the methane to CO and H-2, which then reacts with the iron oxide at a considerably higher rate than methane. Furthermore, no carbon formation or defluidization occurred.