The partial oxidation of methane to synthesis gas (syngas) was performed on a tubular La0.6Sr0.4Co0.2Fe0.8O3-delta membrane reactor packed with a Ni/gamma-Al2O3 catalyst. In 1098-1158 K, the CH4 conversion was larger than 96% with the CO selectivity larger than 97% at low methane concentrations in the feed. CH4 conversion decreased and CO selectivity remained essentially constant with increasing concentration of methane in the feed. Carbon deposition on the surface of the catalyst (with H-2/CO ratio in the product larger than 2) occurred at high CH4 concentration (>6%) in the feed. Analysis of SEM, XRD and EDS on the used membrane showed metal ion reduction/sublimation and segregation of elements on the membrane surfaces, which led to a redistribution of the metal ions across the membrane after being operated in the membrane reactor at the reaction temperature for 3-7 h. (C)2000 Elsevier Science B.V. All rights reserved.