The effect of catalyst support on the activity of Co catalysts has been investigated for the two-step CH4 homologation reaction. The total amount of CH4 per mole of surface Co decomposed at 450 degrees C, in a reaction time of 1 or 3 min, was greater on the Co/Al2O3 catalyst than the Co/SiO2 catalyst. In the subsequent hydrogenation step at 100 degrees C, more of the carbonaceous deposit was hydrogenated on the Co/SiO2 than the Co/Al2O3. The selectivity to C-2(+) hydrocarbons was also higher on the Co/SiO2 catalyst. These results are discussed in terms of the effect of migration of the carbonaceous deposit from the metal to the support, that apparently occurs more readily on the Co/Al2O3 catalyst than on the Co/SiO2 catalyst.