An emergency oxygen supply system (36) for use on aircraft in the event of a loss in cabin pressure is configured for delivering allotments of oxygen and timing the delivery of such allotments to each passenger (16) so as to maximize the efficiency of the transfer of such oxygen into the passengers bloodstream. The delivery of each allotment is selected so that the entire allotment is available for inhalation into the region of he lung most efficient at oxygen transfer while the volume of the allotment is selected to substantially coincide with the volume of such region of the lung.
