Thermo-catalytic decomposition of methane over different carbonaceous materials has been studied using a thermobalance by monitoring the mass gain (the amount of carbon deposited) with time. A kinetic study has been carried out using one carbon black, BP2000, and an activated carbon, CG Norit, to compare the behaviour of two carbon samples of different origin/nature as catalysts for this process. The reaction order of the carbon growth over CG Norit and BP2000 catalysts may be practically said to be 0.5. The activation energies over these catalysts were 141 and 238 kJ/mol, respectively. Methane decomposition reaction over carbon catalysts seems to be controlled by two simultaneous processes: first, decrease in methane decomposition rate due to the blocking of catalytic active sites by the carbon species deposited, and secondly, an increase in methane decomposition rate due to the formation of catalytically active carbon species produced from methane. (C) 2007 Elsevier B.V. All rights reserved.