NOVELTY - Liquefaction of feed gas involves providing at least portion of the total refrigeration required to cool and condense the feed gas by utilizing a first refrigeration system which utilizes at least 2 refrigerant components and provides refrigeration in a first temperature range; and a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream.    USE - For liquefaction of feed to produce liquefied natural gas.    ADVANTAGE - The method exploits the benefits of gas expander cycle in providing cold refrigeration while utilizing the benefits of pure or multi-component vapor recompression refrigeration cycles in providing warm refrigeration. More than 5%, usually more than 10% of the total refrigeration power required for liquefaction of the feed gas can be consumed by the pure or mixed component vapor recompression cycles(s). The method can be implemented in the design of new liquefaction plant or can be utilized as retrofit or expansion of existing plant.    DETAILED DESCRIPTION - Liquefaction of a feed gas involves providing at least a portion of the total refrigeration required to cool and condense the feed gas by utilizing (a) a first refrigeration system comprising recirculating refrigeration circuit(s), where the first refrigeration system utilizes at least 2 refrigerant components and provides refrigeration in a first temperature range; and (b) a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream. The second refrigeration system is operated by compressing a second gaseous refrigerant to provide the pressurized gaseous refrigerant in (b); cooling the pressurized gaseous refrigerant to yield a cooled gaseous refrigerant; work expanding the cooled gaseous refrigerant to provide the cold refrigerant in (b); warming the cold refrigerant to provide refrigeration in the second temperature range; and recirculating the resulting warmed refrigerant to provide the second gaseous refrigerant. The feed gas is natural gas. The resulting liquefied natural gas stream is flashed to lower pressure to yield a light flash vapor and a final liquid product, and the light flash vapor is used to provide the second gaseous refrigerant in the second refrigerant circuit.    DESCRIPTION OF DRAWING(S) - The figure is a schematic flow diagram of a method of liquefying feed gas.    Scrub column (108)    Fractionation section (112)    Turbo-expander (132)    Intercooler compressor (158)    Turbo-expander (166)