The facilitated transport of propylene through immobilized liquid membrane with Ag⁺ as a carrier was investigated. Propylene/methane was used as a model system to study the degree of separation between olefin and paraffin through this liquid membrane. The facilitation ratio of propylene was 20-60 depending on the silver nitrate concentration. The separation factor between the two gases were 50-100 with the amount of silver nitrate used.