A high concentration nasal oxygen mask for delivering high concentrations of oxygen to a patient via the nasal passages of the patient. The high concentration nasal oxygen mask includes a mask portion for enclosing the nose of the patient, an oxygen reserve bag for receiving a supply of oxygen from an external source, a one-way valve for allowing the passage of oxygen in only one direction from the reserve bag to the mask, and a one-way flap to allow the patients expired gases to flow out of the mask without allowing atmospheric gases back into the mask.
