A gas (1) is liquefied by cooling successively through at least two temperature ranges by vaporization of respective refrigerants (117, 213 & 315) with the vaporizing refrigerant providing the coldest temperature range further vaporizing (317) at temperatures above the highest temperature of that range. The partially vaporized refrigerant (316) that provided the coldest temperature range preferably is further vaporized (317) against a compressed return vapor (328) in a recirculating refrigeration system.