La2NiO4 tubular membranes of relative density over 92% were used to separate oxygen from air and facilitate the partial oxidation of methane to H-2 and CO at 900degreesC. When methane was fed into a tube of inner surface area 5.11 cm(2) at a rate of 10.5 ml/min, methane throughput conversion was 89%, CO selectivity 96%, H-2/CO ratio 1.5, and the equivalent oxygen flux was 6.8 ml/min. The surface of the La2NiO4 membrane exposed to CH4 decomposed into La2O3 and Ni, while the surface in contact with air remained almost unchanged. It is suggested that the conversion of methane in the membrane reactor involves the reforming of methane by the H2O and CO2 catalyzed by nickel. (C) 2003 Elsevier B.V. All rights reserved.