The reaction behavior and carbon deposition during the CO2/CH4 reforming reaction have been investigated over the gamma-Al2O3-supported Co catalysts as a function of Co loading (between 2 and 20 wt%) and calcination temperature (T-c = 500 or 1000degreesC). It was found that the stability of Co/gamma-Al2O3 catalysts was strongly dependent on the Co loading and calcination temperature. For some loadings (6 wt% for T-c = 500degreesC and 9 wt% for T-c = 1000degreesC), stable activities have been achieved. However, over the catalysts with high Co loadings (>12 wt%), notable amounts of carbon were accumulated during reforming, and deactivation was observed. Moreover, severe deactivation was also noted over the 2 wt% catalysts, both when carbon deposition occurred (T-c = 500degreesC) or was absent (T-c = 1000degreesC). In the latter case, the oxidation of the metallic sites was responsible for the deactivation. Hence, there are two different deactivation mechanisms, namely, carbon deposition and oxidation of metallic sites. The activities were stable when a balance between carbon formation and its oxidation could be achieved.