Selective oxidation of n-butane to maleic anhydride was studied using a tubular ceramic membrane reactor loaded with a commercial VPO catalyst and under both O-2-rich and butane-rich feed conditions. The study was carried out using a configuration by which butane was fed to the inner tube (tube-side) where the catalyst was mounted and O-2 was fed either entirely to the outer tube (shell-side) or distributed in a certain ratio between the tube- and shell-sides with a variation of the pressure difference across the membrane, Delta P. It was observed that the use of a butane-rich feed under this configuration gives a higher maleic anhydride yield and that both Delta P values and the way feed O-2 was distributed can have a significant effect on the reaction rate.