Respiratory gas delivery apparatus is disclosed that comprises a respiratory mask (30) and a reservoir bag assembly (20). The respiratory mask (30) comprises a mask body (32) defining a cavity, and an inhalation port (42) for enabling passage of gas into the cavity of the mask body (32), the mask body (32) being adapted to fit about the mouth and/or nose of the patient such that respiratory gas can be inhaled by the patient from the cavity. The reservoir bag assembly (20) comprises a flexible bag for containing a reservoir of respiratory gas. The respiratory mask (30) and the reservoir bag assembly (20) are provided with corresponding connectors (60,70) adapted for engagement so as to enable fluid communication between the flexible bag and the respiratory mask (30). The connectors (60,70) are provided with formations (66,78) adapted to interlock upon engagement of the reservoir bag assembly (20) with the respiratory mask (30).
