A comparison has been made of the behaviour in the oxidative coupling of methane of a Ba/CaO catalyst with that of a Li/MgO material. Doping of CaO with BaCO3 resulted in a catalyst which is more active at lower reaction temperatures than is BaCO3. The active oxygen entity in the case of Ba/CaO is probably an O2−2 species. Ba/CaO is more stable but less selective than is Li/MgO. The effect of residence time was studied for both Ba/CaO and Li/MgO. The direct oxidation of methyl radicals to give carbon monoxide and carbon dioxide plays a more important role in the case of Ba/CaO than is the case with Li /MgO.