The potential of room-temperature ionic liquids (RTILs) in separating ethylene from ethane is investigated. The absorption of olefins is enhanced by chemical absorption via p-complex formation with a transition-metal cation added to a standard RTIL. The effects of the ionic liquid structure of silver-based RTILs that contain Ag(I) salts (AgNO3, Ag[TfO], and Ag[Tf2N]) on gas absorption and solvent stability are investigated. The absorption isotherms of C2H4 and C2H6 into standard RTILs and designed silver-based RTILs were measured with a gravimetric balance between 303 and 333 K and up to 10 bar. C2H4 absorption was chemically enhanced in the silver-based RTILs and was considerably higher than that in the standard RTILs. Absorption of C2H6 in the silver-based RTILs is based on physical interactions only. The olefin/paraffin selectivity at a pressure of 1 bar was 30-50 higher in the silver-based RTILs than in standard ionic liquids.