Process for the separation of air by cryogenic distillation in a column system including a high pressure column, a low pressure column, the bottom of the low pressure column being thermally coupled with the top of the high pressure column, an intermediate pressure column, operating a pressure between that of the high pressure column and that of the low pressure column, and an argon column wherein: i) purified compressed air is cooled in a heat exchanger and sent at least in part to the high pressure column, ii) nitrogen enriched liquid (40, 41) is sent from the top of the high pressure column to the top of the low pressure column, iii) oxygen rich liquid is removed from the low pressure column, pressurized and vaporized in the heat exchanger or another heat exchanger, iv) nitrogen rich liquid is removed from the column system, pressurized and vaporized in the heat exchanger or another heat exchanger, v) argon enriched gas is sent from the low pressure column to the argon column, said argon column having a top condenser, and argon rich fluid is removed from the top of the argon column, vi) oxygen enriched liquid from the bottom of the high pressure column is partially vaporized in the top condenser of the argon column and the gas thereby formed is sent to the low pressure column, vii) a liquid air stream or a stream (20, 22) containing between 18 and 25 mol.% oxygen withdrawn from an intermediate point of the high pressure column is sent at least in part to a top condenser of the intermediate pressure column where it is partially vaporized to form a vapor and a liquid, viii) the vapor formed in the top condenser of the intermediate pressure column is sent to the low pressure column, ix) the liquid from the top condenser of the intermediate pressure column is sent to the intermediate pressure column to be separated, x) a liquid from the bottom of the intermediate pressure column is sent to the low pressure column, and xi) a liquid from the top of the intermediate pressure column is sent to the top of the low pressure column. i) purified compressed air is cooled in a heat exchanger and sent at least in part to the high pressure column, ii) nitrogen enriched liquid (40, 41) is sent from the top of the high pressure column to the top of the low pressure column, iii) oxygen rich liquid is removed from the low pressure column, pressurized and vaporized in the heat exchanger or another heat exchanger, iv) nitrogen rich liquid is removed from the column system, pressurized and vaporized in the heat exchanger or another heat exchanger, v) argon enriched gas is sent from the low pressure column to the argon column, said argon column having a top condenser, and argon rich fluid is removed from the top of the argon column, vi) oxygen enriched liquid from the bottom of the high pressure column is partially vaporized in the top condenser of the argon column and the gas thereby formed is sent to the low pressure column, vii) a liquid air stream or a stream (20, 22) containing between 18 and 25 mol.% oxygen withdrawn from an intermediate point of the high pressure column is sent at least in part to a top condenser of the intermediate pressure column where it is partially vaporized to form a vapor and a liquid, viii) the vapor formed in the top condenser of the intermediate pressure column is sent to the low pressure column, ix) the liquid from the top condenser of the intermediate pressure column is sent to the intermediate pressure column to be separated, x) a liquid from the bottom of the intermediate pressure column is sent to the low pressure column, and xi) a liquid from the top of the intermediate pressure column is sent to the top of the low pressure column.