A study of the selective oxidative coupling of methane (OCM) to C-2 hydrocarbons (ethane and ethylene) in a solid-state electrochemical reactor made from yttria-stabilized zirconia (YSZ) has been made. Three different catalyst-electrode systems based on silver and two trimetallic formulations of Mn modified alkali (Na and K) tungstates supported on silica were used. A comparison is made between co-fed and electrochemically-supplied oxygen. The electrochemically-supplied oxygen gave higher overall C-2 selectivities than the co-fed method under low current conditions, which was attributed to differences in local methane to oxygen ratios at the catalyst surface. The potassium tungstate supported catalyst gave the best overall C-2 selectivity (86% at 4% C-2 yield).