CaO-La2O3-MgO and BaO-La2O3-MgO catalysts with different compositions have been studied for their bulk and surface properties (viz. crystal phases, surface area, acidity/acid strength distribution, basicity/oase strength distribution, etc.) and catalytic activity/selectivity in the oxidative coupling of methane (OCM) at different processing conditions (reaction temperature, 700-850 degrees C; CH4/O-2 ratio in feed, 3.0, 4.0 and 8.0 and GHSV, 102000 and 204000 cm(3) g(-1) h(-1)). The surface acidity and strong basicity of La2O3-MgO are found to be increased due to the addition of a third component (CaO or BaO), depending upon its concentration in the catalyst. The addition of CaO or BaO to La2O3-MgO OCM catalyst causes a significant improvement in its performance. Both the CaO- and BaO-containing catalysts show a high activity and selectivity at 800 degrees C, whereas, the activity and selectivity of BaO-containing catalysts at 700 degrees C is lower than that of CaO-containing catalysts.