Supported ionic liquid membranes offer potentially lower-energy alternatives to cryogenic distillation for the separation and isolation of light gas olefins (ethene and propene) which are the only sources of starting materials to make polythene and polypropylene. This study will identify which features of the ionic liquid are responsible for differences in the solubilities of propane and propene in a key model ionic liquid. This will help gain understanding how the gases dissolve in the liquids, providing information that can direct the development of better liquid membranes for energy and cost-efficient recovery of these gases.