A mathematical model has been developed for membrane separation of binary gas mixture for a counter-current now having membrane configurations of nat-sheet and hollow-fibre. A binary gas system of hydrogen and nitrogen has been used to simulate the conditions for the recovery of hydrogen from the purge gas in ammonia plant. Simulation studies showed that the use of counter-current hollow-fibre feed-outside-mode permeator, at higher feed flow rate, and at a high feed pressure as permitted by the mechanical strength of the system, is best for good recovery of hydrogen. It is further observed that while separation from polyimide membrane is superior to cellulose acetate membrane, performance of polystyrene membrane is quite inferior.