Simulation results for an adsorptive gas separation process are presented. A feed gas mixture containing 25 % methane and 75 % hydrogen at a pressure of 20 atm is separated by a four-bed, nine-step pressure swing adsorption process to produce high purity hydrogen. The optimum operating conditions for producing maximum net product are identified. It is shown that improving mass-transfer characteristics of the adsorbent is helpful, but only up to a limit, after which it does not help to further reduce the mass-transfer resistance. It is also shown that the best adsorbent cannot be chosen by considering only the selectivity or working capacity. A combination of both of these properties is important. On the other hand, higher saturation capacity improves the performance of the simulated process.