Dissociative chemisorption of methane over ruthenium, cobalt, and ruthenium-cobalt bimetallic catalysts supported by alumina, silica, and NaY was investigated under a wide range of temperatures. The extent of hydrogen loss from methane was monitored by deuterium uptake of the surface carbonaceous species (CHx) formed from methane and/or by the amount of hydrogen evolved during the course of methane chemisorption. The presence of a high average number of deuteriums in the desorbing methane suggested a wide spread dissociation of methane. The initial distribution of the deuterated products generally decreased in the sequence CD4 > CHD3 > CH2D2. The amount of chemisorbed methane and the evolution of hydrogen during methane chemisorption increase with temperature and follow the sequence of reducibility of the supported metals and the particle size which, in turn, depends on the support and the alloy formed. CH species prevailed on alumina- and silica-supported catalysts, while on NaY-supported metals, CH2 species are dominant when small metal particles are stabilized inside the supercage.