Decomposition of methane into carbon nanotubes over CoO catalysts supported on various catalyst supports at 550 °C and 700 °C was investigated. The effect of catalyst promoters on the supported CoO catalysts at 700 °C was also examined. Electron microscope observations showed that among the various catalyst supports tested, alumina was found to be the most appropriate for CoO that CoO/Al2O3 catalyst grew carbon nanotubes with significant hollow cores. Experimental results further revealed that introducing FeO into CoO/Al2O3 catalyst resulted in the formation of carbon nanotubes with thin wall structure. Introducing MoO into CoO/Al2O3 catalyst increased the carbon capacity and the selectivity of CoO/Al2O3 catalyst in growing better quality carbon nanotubes.