SEP-P-3239 A facilitated liquid membrane for the separation of olefins from a gaseous feed stream comprises a porous support structure (10, 15) and a liquid membrane which comprises an aqueous solution containing a metal salt facilitatorcapable of coordinating with olefin gases, and an alkyl carbonate co-solvent. A process for the separation of olefins from gaseous feed streams comprises the steps of passing a gaseous feed stream over one side of a facilitated liquid membrane according to the present invention and collecting the olefins on the other side of the membrane.