Herein, data available in the literature for nonoxidative, two-step CH4 homologation over SiO2-supported transition metals are analyzed according to the principle of Sabatier, Volcano plots are constructed which provide empirical evidence to support the hypothesis that the metal-carbon bond strength is pivotal to determine catalyst efficiency, chain-growth probability, and selectivity to C-2(+) hydrocarbons. (C) 2000 Academic Press.