Studies on bi-alkaline earth composite catalysts indicate that these new catalytic systems have high activity and selectivity for methane oxidative coupling. Of the above-mentioned catalysts, MgO/BaCO3 composite catalyst possesses the highest activity and selectivity. In a comparison of single component samples with the MgO/BaCO3 catalyst, it is shown that there is considerable interaction between the two components in the catalyst. The interaction leads the MgO/BaCO3 catalyst to have the correct O2(2)- ion concentration and their distribution, lower lattice oxygen mobility, strong basicity of surface and lower specific surface areas to favor OCM.A C2 yield of 16.3% and selectivity of 68% was obtained at 1053 K, CH4/air = 1, GHSV = 3.88 X 10(4) h-1 over 0.25 g 62 mol% MgO/BaCO3 catalyst during a 530 h stability test. Studies of the reaction conditions indicate that a C, yield higher than 18% could be obtained under properly selected reaction conditions. Experiments using a 26.4-mm diameter fixed-bed reactor with 10 ml MgO/BaCO3 catalyst show that a C2 yield of 16.3% and a C2 selectivity of 65% was obtained with a catalyst bed temperature of ca. 1200 K, CH4/O2 = 5 and methane GHSV = 5000 h-1 with 1.8 ml/min water as a diluent.