Abstract: A method of producing a methane-rich liquid stream from a stream of natural gas predominantly consisting of methane and also containing nitrogen, entailing:(a) supplying said natural gas stream at a pressure above atmospheric pressure,(b) cooling and liquefying said natural gas stream using one or more refrigeration cycles, and(c) expanding said liquefied natural gas to lower pressure in two or more stages in series, phase separating the gas and liquid phases produced during the expansion, thereby concentrating the nitrogen into the vapor phase, and producing a methane-rich liquefied natural gas.