Abstract: Systems for storing and dispensing gases. The gas storage systems are two-phase gas/solid or gas/liquid, or three-phase gas/liquid/solid, functioning by reversible sorption. In gas storage systems having a solid phase, use is made of a polymeric material, preferably a hydrogel, having microvoids functioning as interstitial stores for gas. Reversible gas sorption in the microporous polymer is improved by treatment with a swelling promoter. The stored gas may be a propellant, and reversible sorption propellant storage may be used in all types of pressure pack dispenser. Cryogenic techniques facilitate preparation of propellant systems with standardized parameters. The invention enables use of safe and environmentally benign gases as propellants.