Numerous studies have been conducted in recent years on the partial oxidation of methane to synthesis gas (syngas : CO + H-2) with air as the oxidant. In partial oxidation, a mixed-oxide ceramic membrane selectively transports oxygen from the air; this transport is driven by the oxygen potential gradient, Of the several ceramic materials we have tested, a mixed oxide based on the Sr-Fe-Co-O system has been found to be very attractive. Extensive oxygen permeability data have been obtained for this material in methane conversion experiments carried out in a reactor, The data have been analyzed by a transport equation based on the phenomenological theory of diffusion under oxygen potential gradients. Thermodynamic calculations were used to estimate the driving force for the transport of oxygen ions, The results show that the transport equation deduced from the literature describes the permeability data reasonably well and can be used to determine the effective or ambipolar diffusion coefficients and the associated activation energy of oxygen ions in the ceramic membrane material.