Compression train for a natural gas liquefaction process, the compression train comprising: a driver machine; only one centrifugal compressor machine driven in rotation by said driver machine; the compressor being configured to compress a refrigerant gas with a molecular weight less than 30 g/mol from a suction pressure to a discharge pressure; wherein the ratio between discharge and suction pressures is higher than 10, preferably higher than 12, more preferably higher than 15; wherein the compressor machine comprises a plurality of stages of compression split in two or three sections of compression (523,524) with all sections of compression (523, 524) arranged in the only one centrifugal compressor machine having a single casing and wherein the compressor machine comprises an inlet (519, 522) and an outlet (521, 520) for each section of compression (523, 524); wherein the compressor machine is of barrel-type and the two or more sections of compression (523, 524) are arranged in a common bundle removably insertable in a common casing; wherein each stage of compression comprises an impeller (507, 508, 509, 510, 511) and wherein the impellers have constant or decreasing diameters and the last impeller has a smaller diameter with respect to the first one; and wherein the most upstream impellers (507, 508) are open-type impellers and the other impellers (509, 510, 511) are closed-type impellers with all of the impellers (507, 508, 509, 510, 511) stacked one on the other to form a rotor, wherein the sections of compression are three, the third section is arranged downstream the second one which in turn is arranged downstream the first one, the outlet of the first section is indirectly fluidly connected to the inlet of the second section of compression, and the outlet of the second section is indirectly fluidly connected to the inlet of the third section of compression; wherein the gas refrigerant passes through an intercooler between an outlet and the subsequent inlet. a driver machine; only one centrifugal compressor machine driven in rotation by said driver machine; the compressor being configured to compress a refrigerant gas with a molecular weight less than 30 g/mol from a suction pressure to a discharge pressure; wherein the ratio between discharge and suction pressures is higher than 10, preferably higher than 12, more preferably higher than 15; wherein the compressor machine comprises a plurality of stages of compression split in two or three sections of compression (523,524) with all sections of compression (523, 524) arranged in the only one centrifugal compressor machine having a single casing and wherein the compressor machine comprises an inlet (519, 522) and an outlet (521, 520) for each section of compression (523, 524); wherein the compressor machine is of barrel-type and the two or more sections of compression (523, 524) are arranged in a common bundle removably insertable in a common casing; wherein each stage of compression comprises an impeller (507, 508, 509, 510, 511) and wherein the impellers have constant or decreasing diameters and the last impeller has a smaller diameter with respect to the first one; and wherein the most upstream impellers (507, 508) are open-type impellers and the other impellers (509, 510, 511) are closed-type impellers with all of the impellers (507, 508, 509, 510, 511) stacked one on the other to form a rotor, wherein the sections of compression are three, the third section is arranged downstream the second one which in turn is arranged downstream the first one, the outlet of the first section is indirectly fluidly connected to the inlet of the second section of compression, and the outlet of the second section is indirectly fluidly connected to the inlet of the third section of compression; wherein the gas refrigerant passes through an intercooler between an outlet and the subsequent inlet.