Ionic-electronic mixed-conducting perovskite-type oxide La0.6Sr0.4Co0.8Fe0.2O3 was applied as a dense membrane for oxygen supply in a reactor for methane coupling. The oxygen permeation properties were studied in the p(O2)-range of 10(-3)-1 bar at 1073-1273 K, using helium as a sweeping gas at the permeate side of the membrane. The oxygen semi-permeability has a value close to 1 mmol m(-2) s(-1) at 1173 K with a corresponding activation energy of 130-140 kJ/mol. The oxygen flux is limited by a surface process at the permeate side of the membrane. It was found that the oxygen flux is only slightly enhanced if methane is admired with helium. Methane is converted to ethane and ethene with selectivities up to 70%, albeit that conversions are low, typically 1-3% at 1073-1173 K. When oxygen was admired with methane rather than supplied through the membrane, selectivities obtained were found to be in the range 30-35%. Segregation of strontium was found at both sides of the membrane, being seriously affected by the presence of an oxygen pressure gradient across it. The importance of a surface limited oxygen flux for application of perovskite membranes for methane coupling is emphasized.