Heterogeneous stoichiometric oxidation and catalytic partial oxidation (CPO) of methane are studied at the surfaces of MgO, alpha-Al2O3, and CeO2 containing small Rh clusters. Stoichiometric reactions are linked to a repeating loop that has produced the CPO of methane at temperatures lower than 773 K with selectivity close to 100%. These reactions occur through the formation and the thermal decomposition of hydridocarbonyl Rh clusters. Molecular aspects of stoichiometric reactions are compared with those produced under stationary conditions with flows of premixed CH4 and O-2 at very short residence time. Comparisons show that collisions between hydridocarbonyl clusters and gaseous O-2 produce CO2 and H2O. IR thermography maps collected during short residence time CPO and gaseous temperature measurements are also reported. They show the existence of nonlocal thermal equilibrium between the solid and gaseous phases. (C) 2000 Academic Press.