MFI-type lozenge zeolitic membranes were prepared by a vapor-phase transport method on porous or-alumina flat disks. Pure or mixed gas permeation measurements of butane isomers were performed at 375 K using two methods: pressure gradient (PG) and concentration gradient (CG) methods. Pure gas permeation measurements of H-2, He, CH4, N-2, O-2, CO2 and SF6 were also carried out using PG method. Counter-diffusion of helium as a sweep gas was evaluated by determining the gas composition at the outlet of the feed side. It was confirmed that the counter-diffusion of helium occurs only when the total pressure of the feed side was <80 kPa. In the mixed gas permeation measurements, the value of separation factor depended on the method of gas permeation. The separation factors of n-butane to i-butane were ca. 10 in the PG method and 30-60 in the CG method. (C) 2000 Elsevier Science B.V. All rights reserved.