A four-step pressure swing adsorption (PSA) process for air drying on a silicagel dessicant is considered. The effects of hysteresis in adsorption/desorption equilibrium isotherms and of loading dependence of the effective diffusion coefficient on the process performance are investigated on a mathematical model. A. comparative parametric study reveals that for identical operating conditions, hysteresis can be detrimental to product purity. Multiplicity of cyclic steady states is shown to exist as a result of hysteresis. A transient regime invoked by a gradual change in the inlet air humidity is discussed.