The influence of morphology of the support particles upon the nickel-catalyzed decomposition of methane into carbon nanotubes and hydrogen was explored using a thermogravimetric apparatus. High carbon nanotube yield was attained by the Ni catalysts supported on the glycothermally synthesized ZrO2 and Er3Ga5O12 particles, which had spherical shapes. Quite high carbon yield was also obtained by the Ni catalyst supported on spherical Al2O3 particles (Nanophase Tech. Corp.). It was concluded that the most important factor governing the carbon yield is the morphology of the catalyst support, which contributes to the internal pressure of carbon nanotubes thus determining their chemical potentials.