Results of an experimental and theoretical study of a parallel passage adsorbent contactor are reported. Theoretical considerations suggest that such an adsorber should be preferable to the traditional packed bed for application in which pressure drop is important. An expression for the HETP (height equivalent to a theoretical plate) for a parallel passage contactor, analogous to the van Deemter equation for the packed bed [1], is derived and verified experimentally for the adsorption of several light gases from a helium carrier in an adsorber consisting of parallel sheets of activated carbon fibre adsorbent. The extension to a multiple passage system and the effect of moisture in the feed gas were also investigated. A high selectivity ratio (alpha(CO2/N2)) and a diffusion constant of about 10 ms for adsorption of CO2 and N-2 on ACF adsorbent confirm that such a parallel-sided duct coated with ACF sheets would be well suited to a dual piston rapid pressure swing adsorption system for large throughput and low value added applications such as CO2 removal from stack gas. (C) 1997 Elsevier Science B.V.