Abstract: The improved high pressure oxygen-saturated water treatment apparatus of the present invention functions to provide super-saturated oxygen treatment to waste water for purification thereof. The apparatus includes a pressurized treatment tank having a substantial longitudinal dimension, with a chamber separation plate forming two interconnected chambers in the tank. An input conduit for flowing waste water into the first chamber of the tank is provided. An oxygen input conduit is connected to the tank for providing oxygen-containing gas under substantial pressure within the tank. An oxygen output conduit is also disposed on the tank for receiving the oxygen-containing gas from the tank to form a pressurized oxygen-containing stream.