A portable oxygen supply unit for breathable air with an enhanced oxygen content has a tilt valve in a mounting cup on a pressurized container containing medical or aviators oxygen. A hollow housing is sealed to the mounting cup. The hollow housing is flowably connected to a mouthpiece and to an inlet for ambient air. A user can open the tilt valve with an actuator that is slidable in the hollow housing. When the valve is open, the pressurized oxygen flows into the hollow housing. As the user inhales through the mouthpiece the oxygen released from the container is diluted with ambient air drawn through the inlet for efficient use of the oxygen dispensed from the container.