A method of liquefying a natural gas feed stream to produce a liquefied natural gas (LNG) 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 <EOS>