A method of liquefying a natural gas feed stream to produce a liquefied natural gas product, the method comprising: (a) liquefying the natural gas feed stream, by indirect heat exchange with a methane or natural gas refrigerant circulating as gaseous refrigerant in a gaseous expander cycle, to produce a first LNG stream; (b) expanding the first LNG stream to further cool and partially vaporize said stream, and separating the resulting vapor and liquid phases to produce a first flash gas stream and a second LNG stream; (c) expanding the second LNG stream to further cool and partially vaporize said stream, and separating the resulting vapor and liquid phases to produce a second flash gas stream and a third LNG stream, the LNG product comprising the third LNG stream or a portion thereof; and (d) recovering refrigeration from the second flash gas stream, wherein said second flash gas stream is used to sub-cool, by indirect heat exchange a first supplementary LNG stream, at least a portion of which is then expanded and separated to produce additional vapor and liquid for forming, respectively, the second flash gas stream and third LNG stream; the method further comprising: (e) expanding the third LNG stream to further cool and partially vaporize said stream, and separating the resulting vapor and liquid phases to produce a third flash gas stream and a fourth LNG stream, the LNG product comprising the fourth LNG stream or a portion thereof; and (f) recovering refrigeration from the third flash gas stream characterized in that said third flash gas stream is used to sub-cool, by indirect heat exchange a second supplementary LNG stream, formed from a sub-cooled portion of the first supplementary LNG stream, at least a portion of which is then expanded and separated to produce additional vapor and liquid for forming, respectively, the third flash gas stream and fourth LNG stream. (a) liquefying the natural gas feed stream, by indirect heat exchange with a methane or natural gas refrigerant circulating as gaseous refrigerant in a gaseous expander cycle, to produce a first LNG stream; (b) expanding the first LNG stream to further cool and partially vaporize said stream, and separating the resulting vapor and liquid phases to produce a first flash gas stream and a second LNG stream; (c) expanding the second LNG stream to further cool and partially vaporize said stream, and separating the resulting vapor and liquid phases to produce a second flash gas stream and a third LNG stream, the LNG product comprising the third LNG stream or a portion thereof; and (d) recovering refrigeration from the second flash gas stream, wherein said second flash gas stream is used to sub-cool, by indirect heat exchange a first supplementary LNG stream, at least a portion of which is then expanded and separated to produce additional vapor and liquid for forming, respectively, the second flash gas stream and third LNG stream; the method further comprising: (e) expanding the third LNG stream to further cool and partially vaporize said stream, and separating the resulting vapor and liquid phases to produce a third flash gas stream and a fourth LNG stream, the LNG product comprising the fourth LNG stream or a portion thereof; and (f) recovering refrigeration from the third flash gas stream characterized in that