Alkali metal (viz. Li, Na, K, Rb and Cs) promoted MgO catalysts (with an alkali metal/Mg ratio of 0.1) calcined at 750 degrees C have been compared for their surface properties (viz. surface area, morphology, acidity and acid strength distribution, basicity and base strength distribution, etc.) and catalytic activity/selectivity in the oxidative coupling of methane (OCM) to C-2-hydrocarbons at different temperatures (700-750 degrees C), CH4/O-2 ratios (4.0 and 8.0) in feed, and space velocities (10320 cm(3) g(-1) h(-1)). The surface and catalytic properties of alkali metal promoted MgO catalysts are found to be strongly influenced by the alkali metal promoter and the calcination temperature of the catalysts. A close relationship between the surface density of strong basic sites and the rate of C-2-hydrocarbons formation per unit surface area of the catalysts has been observed. Among the catalysts calcined at 750 degrees C, the best performance in the OCM is shown by Li-MgO (at 750 degrees C).