A device for delivering diluted oxygen to a patient, the device comprising: an inner chamber and an outer chamber, the outer chamber comprising an outer chamber opening and the inner chamber comprising first and second oxygen ports (1a - 1g) and air entrainment windows (112, 114), for entraining room air received from the outer chamber with oxygen entering the inner chamber; each of the first and second oxygen ports (1a-1g) being configured to couple an oxygen tube connector (412; 612) to the device, the oxygen tube connector (412; 612) being configured to deliver oxygen from an oxygen source; the first oxygen port (1a - 1g) configured to deliver a first oxygen concentration to the patient when connected to the oxygen tube connector (412; 612), and the second oxygen port (1a-1g) configured to deliver a second oxygen concentration to the patient when connected to the oxygen tube connector (412; 612), wherein each oxygen port (1a-1g) comprises an orifice (3a-3g), each orifice having a size that pertains to a particular oxygen concentration, wherein the size of each orifice (3a-3g) determines (i) a velocity of oxygen, at a flow rate, entering the inner chamber through the respective orifice (3a - 3g) when the oxygen tube connector (412; 612) is connected to the corresponding oxygen port (1a-1g), and (ii) the amount of room air entrained through the windows (112; 114) from the outer chamber into the inner chamber when the oxygen tube connector (412; 612) is connected to the corresponding oxygen port (1a-1g), to achieve delivery of the corresponding particular oxygen concentration by the device, wherein the device is structured to enable selectively altering the oxygen concentration delivered by the device from the first concentration to the second concentration by removing the oxygen tube connector (412; 612) from the oxygen port (1a-1g) pertaining to the first oxygen concentration and connecting the oxygen tube connector (412; 612) with the oxygen port (1a-1g) pertaining to the second oxygen concentration, characterised in that: the device is structured such that, in use, room air can enter the inner chamber through any of the first oxygen port (1a - 1g) and the second oxygen port (1a - 1g) that is not connected to an oxygen tube connector. an inner chamber and an outer chamber, the outer chamber comprising an outer chamber opening and the inner chamber comprising first and second oxygen ports (1a - 1g) and air entrainment windows (112, 114), for entraining room air received from the outer chamber with oxygen entering the inner chamber; each of the first and second oxygen ports (1a-1g) being configured to couple an oxygen tube connector (412; 612) to the device, the oxygen tube connector (412; 612) being configured to deliver oxygen from an oxygen source; the first oxygen port (1a - 1g) configured to deliver a first oxygen concentration to the patient when connected to the oxygen tube connector (412; 612), and the second oxygen port (1a-1g) configured to deliver a second oxygen concentration to the patient when connected to the oxygen tube connector (412; 612), wherein each oxygen port (1a-1g) comprises an orifice (3a-3g), each orifice having a size that pertains to a particular oxygen concentration, wherein the size of each orifice (3a-3g) determines (i) a velocity of oxygen, at a flow rate, entering the inner chamber through the respective orifice (3a - 3g) when the oxygen tube connector (412; 612) is connected to the corresponding oxygen port (1a-1g), and (ii) the amount of room air entrained through the windows (112; 114) from the outer chamber into the inner chamber when the oxygen tube connector (412; 612) is connected to the corresponding oxygen port (1a-1g), to achieve delivery of the corresponding particular oxygen concentration by the device, wherein the device is structured to enable selectively altering the oxygen concentration delivered by the device from the first concentration to the second concentration by removing the oxygen tube connector (412; 612) from the oxygen port (1a-1g) pertaining to the first oxygen concentration and connecting the oxygen tube connector (412; 612) with the oxygen port (1a-1g) pertaining to the second oxygen concentration, characterised in that: the device is structured such that, in use, room air can enter the inner chamber through any of the first oxygen port (1a - 1g) and the second oxygen port (1a - 1g) that is not connected to an oxygen tube connector.