Abstract: An improved gas diffuser tube assembly, particularly for diffusing bubbles of oxygen gas into liquid sewage during treatment thereof, is provided. The assembly is characterized by a construction which creates substantially the smallest bubbles that would be operationally practical and which satisfactorily prevents back flow of liquid into the diffuser assembly by including the following. An inner support tube has apertures extending radially therethrough in a bottom portion thereof for passing gas from the inside to the outside thereof. A flexible membrane surrounds the support tube and has a plurality of minute punctures extending therethrough and located in an upper section thereof for receiving the gas which passes between the support tube and the membrane and discharging the gas under pressure out of the membrane sheath in the form of fine streams of tiny bubbles of the gas.