Abstract: A gas-powered, pneumatic ventilator (1) is driven by compressed air from a compressor (2) and its outlet (11) is connected via corrugated tubing (30) to a patient valve (34) and face mask or the like. A source (4) of pure oxygen, such as from an oxygen cylinder (40), is connected via small bore tubing (38) to a gas inlet (37) adjacent the air inlet (33) of the patient valve (34) so that supplementary oxygen is mixed with the air. The patient valve (34) closes and a patient dump valve (16) in the ventilator opens during the exhalation phase to allow oxygen supplied to the patient valve (34) to fill the corrugated tubing (30) from the patient end (32) and displace air in the tubing out of the patient dump valve (16) so that a volume of oxygen is collected in the tubing and is dispensed to the patient during the next inspiratory phase.