The invention concerns a nasal gas-delivery system (21) to be connected to a nose of a patient for delivering a respiratory gas to the patients nostrils, comprising a hollow body (22) with an inner chamber (22a) and an inlet (22b) for receiving a respiratory gas, and a pair of hollow nasal prongs (23, 24), each nasal prongs comprising at least one inner channel (23b, 23c 24b, 24c), in fluid communication with the inner chamber 22a of the hollow body (22). The pair of nasal prongs (23, 24) is surrounded by a pair of flexible flange structures (25, 26), the flange structures (25, 26) being joined by a flexible separation wall (27). The flexible flange structures (25, 26) and the flexible separation wall (27) are configured and sized so as to come into contact with outer portions of the nose of the patient thereby creating a gas tight connection in-between, when the nasal gas-delivery is connected to the nose of the patient with the pair of nasal prongs (23, 24) inserted into the patients nostrils. The nasal gas-delivery system is suitable for delivering gas in the frame of a nasal high flow therapy.
