A life-support system for an aircraft B includes a first oxygen supply apparatus A operable to provide a limited supply of first product gas being one of pure oxygen and oxygen enriched gas, to a breathing gas supply apparatus 12, 13, 14, and a second oxygen supply apparatus B operable to supply a durable supply of second product gas which is an oxygen enriched gas containing a lower concentration of oxygen than that in the first product gas, to the breathing gas supply apparatus 12, 13, 14, wherein the second product gas is supplied as the pressure which is higher than that at which the first product gas is supplied to the breathing gas supply apparatus 12, 13, 14.