The permeability and diffusivity properties of four gases-oxygen, nitrogen, carbon dioxide and methane-have been obtained for membranes prepared by the photocrosslinking of a mixture of chlorosulfonated polyethylene, acting as a binder, and a series of acrylic and methacrylic monomers. These measurements have been per-formed in the range 20degreesC to 50degreesC, and the activation energies have also been determined. These data are presented in comparison with those previously obtained in a crosslinked system in which the binder was not chlorosulfonated polyethylene but an aliphatic polyurethane. Both polymeric systems show similar permselectivities for the gas pairs O-2/N-2 (near 5) and CO2/CH4 (near 12), though overall permeability is about three times lower in the chlorosulfonated polyethylene-based polymer because of the smaller diffusion coefficients. The permeation and diffusion results are discussed in terms of the final structure of the photocrosslinked polymeric system, and it is concluded that it is the binder which is mostly responsible for the gas transport properties of these crosslinked materials.