A PROCESS FOR LIQUEFYING HYDROGEN, HELIUM AND NEON MORE EFFICIENTLY AND ECONOMICALLY THAN BY METHODS PREVIOUSLY PRACTICED, WHICH PROCESS INCLUDES THE STEPS OF COMPRESSING THE GAS (HYDROGEN, HELIUM OR NEON) TO A PRESSURE SUCH THAT, UPON ISOBARICALLY COOLING THE THUS COMPRESSED GAS, A TEMPERATURE ABOVE THE CRTITCAL TEMPERATURE OF THE GAS IS REACHED AT WHICH THE GAS CAN BE ISENTRIOPICALLY EXPANDED TO YIELD SUBSTANTIALLY A SINGLE LIQUID PHASE AT ATMOSPHERIC PRESSURE; THEN ISOBARICALLY COOLING THE GAS AT THIS PRESSURE TO SUCH TEMPERATURE; AND FINALLY ISENTROPICALLY EXPANDING THE GAS TO SUBSTANTIALLY ATMOSPHERIC PRESSURE THROUGH A WORK ENGINE.