Abstract.Recent results on surface reaction steps in the oxidative coupling of methane (OCM) obtained from (1) transient experiments and ( 2 ) a microkinetic analysis are summarized. The interaction of methane and oxygen with MgO and S m 2 0 3 surfaces was investigated by applying H/D-and oxygen-isotope-exchange reactions. The role of short-lived adsorbed oxygen species in methane activation and product formation over MgO and Sm20? catalysts is discussed. Furthermore, elementary reaction steps and their rate constants are derived for the oxidative conversion of methane to COX and ethane from kinetic data for different (CaO) (CeO,), --x catalysts; the rate constants are related to the solid's properties, i.e., electron and 02? conductivity.