The goal of the paper was to investigate the effect of the catalyst precursor on the catalytic activity. For this reason, the structure, the reducibility and the reaction behavior of gamma -Al2O3-supported Co (24 wt%) catalysts as a function of calcination temperature (T-c) were investigated using X-ray diffraction, temperature-programmed reduction, CO chemisorption, pulse reaction with pure CH4, and the catalytic reactions of methane conversion to synthesis gas. Depending on T-c, one, two, or three of the following Co-containing compounds, Co3O4, Co2AlO4, and CoAl2O4, were identified. Their reducibility decreased in the sequence: Co3O4 > Co2AlO4 > CoAl2O4. Co3O4 was generated as a major phase at a T-c of 500 degreesC and Co2AlO4 and CoAl2O4 at a T-c of 1000 degreesC. The reduced Co/gamma -Al2O3 catalysts, obtained via the reduction of the 500 and 1000 degreesC calcined catalysts, provided high and stable activities for the partial oxidation of methane and the combined partial oxidation and CO2 reforming of methane. They deactivated, however, rapidly in the CO2 reforming of methane. Possible explanations for the stability are provided.