Method of liquefying a feed stream comprising a gaseous hydrocarbon stream such as natural gas, the method at least comprising the steps of: (a) providing the feed stream; (b) first cooling the feed stream in one or more first heat exchangers against a first cooling refrigerant being cycled in a first cooling refrigerant circuit, thereby obtaining a cooled gas stream, wherein the first cooling refrigerant comprises > 90 mol% propane; (c) second cooling the cooled gas stream obtained in step (b) into a liquid against a first mixed refrigerant being cycled in a first mixed refrigerant circuit, wherein said second cooling is in two or more heat exchangers (42, 44) arranged in series such that the cooled gas stream passes through each heat exchanger, at least two of which, a second heat exchanger and a third heat exchanger, are operating at different pressures and are supplied with cooling by the first mixed refrigerant in the first mixed refrigerant circuit at different pressures, thereby obtaining a liquefied stream; and (d) sub-cooling the liquefied stream obtained in step (c) against a second mixed refrigerant or against a nitrogen refrigerant being cycled in a sub-cooling refrigerant circuit against a fourth heat exchanger, thereby obtaining a sub-cooled hydrocarbon stream; wherein in step (c) the circulation of the first mixed refrigerant comprises compressing, cooling, and separating the refrigerant into a subsequent first high pressure fraction and a subsequent second low pressure fraction, evaporation of the first and second fractions in different heat exchangers (42, 44), and recollecting of the first evaporated fraction and the second evaporated fraction, wherein the high pressure fraction is evaporated at a higher temperature than the low pressure fraction, characterized in that the cooled gas stream from the second heat exchanger in step (c) passes through a separation vessel, so as to provide a lighter gas stream, being methane-enriched, and a heavier liquid stream, which lighter gas stream is passed to the third heat exchanger. (a) providing the feed stream; (b) first cooling the feed stream in one or more first heat exchangers against a first cooling refrigerant being cycled in a first cooling refrigerant circuit, thereby obtaining a cooled gas stream, wherein the first cooling refrigerant comprises > 90 mol% propane; (c) second cooling the cooled gas stream obtained in step (b) into a liquid against a first mixed refrigerant being cycled in a first mixed refrigerant circuit, wherein said second cooling is in two or more heat exchangers (42, 44) arranged in series such that the cooled gas stream passes through each heat exchanger, at least two of which, a second heat exchanger and a third heat exchanger, are operating at different pressures and are supplied with cooling by the first mixed refrigerant in the first mixed refrigerant circuit at different pressures, thereby obtaining a liquefied stream; and (d) sub-cooling the liquefied stream obtained in step (c) against a second mixed refrigerant or against a nitrogen refrigerant being cycled in a sub-cooling refrigerant circuit against a fourth heat exchanger, thereby obtaining a sub-cooled hydrocarbon stream;