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Dense planar and tubular oxygen separation membranes of La 0.6Ca0.4Fe0.75Co0.25O3-d were investigated as reactors for the partial oxidation (POX) of methane to syngas. Disk-shaped membranes were prepared by compaction and tubes by extrusion. Their permeation properties were measured in an air/argon pO2 gradient as a function of temperature. At 900°C, the oxygen flux through a 1.26 mm thick membrane was 0.075 micromol/cm2s and through a 0.25 mm thick tube, 0.24 micromol/cm2s. For the POX measurements, a catalyst was added to the membrane and methane was introduced on the argon side. This resulted in a gradual increase of the oxygen flux with increasing concentration of methane, reaching 2micromol/ cm2s at 900°C with pure methane. The catalytic properties of the POX reactors were characterised as a function of the methane content. For the planar reactor, the CO selectivity reached 99% and the CH4 conversion 75% at 918°C with pure methane. For the tubular reactor, the CO selectivity and CH4 conversion were respectively 83 and 99% for the same conditions. In all cases the H2/CO ratio was about 2. After 1’400 hours of operation in a tubular POX-reactor, the membrane was examined revealing phase demixing and local decomposition.