This article focuses on the catalytic behavior of MO–Sm2O3 (M = Zn, Mg, Ca, Sr) mixed oxides. The obtained results could be interpreted in terms of solid acid–base catalysis. The mixed oxides were prepared starting from the tartarate complexes of the constituent metals. The concentration as well as the evolution of surface carbonate species with the nature of MO and reaction temperature were analyzed by XRD and TPD methods. The amount of surface basic sites responsible for the formation of C2+ was determined by measuring the amount of evolved CO2 in the 300–800 °C temperature range. The catalytic behavior of the investigated mixed oxides was expressed in terms of methane yield to C2+ and the concentration of CO2 in reaction mixture. The conclusion is that C2+ is formed on the basic sites whereas the acidic sites are responsible for nonselective oxidation of methane to CO2.