A reactor module, consisting of six gas-tight hollow fibre membranes made of the mixed ionic–electronic conducting perovskite, $ {\text{La}}_{{0.6}} {\text{Sr}}_{{0.4}} {\text{Co}}_{{0.2}} {\text{Fe}}_{{0.8}} {\text{O}}_{{3 - \delta }} $ {\text{La}}_{{0.6}} {\text{Sr}}_{{0.4}} {\text{Co}}_{{0.2}} {\text{Fe}}_{{0.8}} {\text{O}}_{{3 - \delta }} , has been tested for oxygen permeation and stability during methane oxidation in the temperature range of 540 to 960°C. Rigorous leak testing was undertaken and it was demonstrated that the module could be adequately sealed. Oxygen permeation fluxes were similar to those reported by previous workers. At higher temperatures of operation, it appeared that mass transfer limited the oxygen flux, as this flux was dependent upon the flow rates on either side of the membrane. In this way, reactant flow rates could be used to manipulate the transmembrane oxygen flux. It was found that the product distribution on the methane side was dependent upon this flux, with carbon monoxide and hydrogen production being favoured at low fluxes and carbon dioxide and water production being favoured at higher fluxes. Furthermore, at low oxygen flow rates, periodic increases in the transmembrane oxygen flux were observed. The cause of this behaviour is unclear but may be as a result of phase/stoichiometric changes associated with the membrane material.