Carbon dioxide reforming of methane has been studied over two ruthenium catalysts supported on silica and on gamma-alumina. Catalytic activity measurements, infrared spectroscopic analysis and isotopic tracing experiments applied to the study of the surface hydroxyl groups of the supports have allowed different reaction mechanisms to be proposed on the bases of the detected surface species, their mobility, stability and reactivity. Activation of both reactants takes place on the ruthenium surface for Ru/SiO2 catalyst. The accumulation of carbon adspecies formed from methane decomposition on the metallic particles finally impedes carbon dioxide dissociation and induces rapid deactivation of this catalyst. The alumina support provides an alternate route for CO2 activation by producing formate intermediates on its surface that subsequently decompose releasing CO. This bifunctional mechanism, in which the hydroxyl groups of the support play a key role, induces greater stability on the Ru/Al2O3 catalyst by significantly decreasing the rate of carbon deposition on the metal. The proposed reaction pathway requires continuous surface mobility of species from the metal to the support and vice versa.