The catalytic activity and selectivity of La2O3 and alkaline earth (viz. Mg, Ca, Sr and Ba) promoted La2O3 (alkaline earth metal/La = Ol)catalysts in the oxidative coupling of methane (OCM) to C-2-hydrocarbons (at 800 degrees C, CH4/O-2 ratio = 4 or 8 and gas hourly space velocity = 102 000 cm(3) g(-1) h(-1)) have been investigated. The acidity and basicity distributions on these catalysts are measured by the temperature programmed desorption (TPD) of NH, and CO2 from 50 degrees C to 950 degrees C, respectively. Both the acidity and basicity of the La2O3 catalysts and their activity in the OCM are strongly influenced by the alkaline earth promoter and its concentration. Among the catalysts, Sr-promoted La2O3 (Sr/La = 0.1) is the most active and selective catalyst for the OCM process. This catalyst contains a larger number of strong basic sites and intermediate strength acid sites.