NOVELTY - An electrolyzer system comprises a pressure vessel having an interior cavity, an electrolyzer located in the interior cavity of pressure vessel, and a pressurized water source to supply pressurized water. The pressurized water in the interior cavity of pressure vessel is supplied to both sides of electrolyzer. The electrolyzer utilizes the pressurized water along with an electrical current to produce hydrogen- and oxygen-containing streams.    USE - For producing hydrogen and/or oxygen.    ADVANTAGE - The inventive electrolyzer system produces hydrogen and/or oxygen at high pressure.    DETAILED DESCRIPTION - An electrolyzer system comprises a pressure vessel (26) having an interior cavity (24), an electrolyzer (22) located in the interior cavity of pressure vessel, a pressurized water source (36) to selectively supply pressurized water, and a flow path from the pressurized water source to the interior cavity of pressure vessel. The electrolyzer has first and second sides. One of the first and second sides is an anode side and the other side is a cathode side. The electrolyzer converts water and electricity into a hydrogen-containing stream on the cathode side and an oxygen-containing stream on the anode side. The interior cavity receives pressurized water from the pressurized water source via the flow path, and the pressurized water pressurizes the interior cavity of pressure vessel. The pressurized water in the interior cavity of pressure vessel is supplied to both sides of the electrolyzer. The electrolyzer utilizes the pressurized water along with an electrical current to produce the hydrogen-containing stream and the oxygen-containing stream. An INDEPENDENT CLAIM is also included for a method of operating an electrolyzer system by positioning an electrolyzer in an interior cavity of a pressure vessel, pressurizing the interior cavity of pressure vessel, supplying water to the first and second sides of electrolyzer, supplying an electrical current to the electrolyzer, producing a hydrogen-containing stream in the cathode side and an oxygen-containing stream in the anode side from the current and water, and regulating a pressure in the first side of electrolyzer by selectively venting a first side stream produced in the first side of electrolyzer out of the pressure vessel and into a pressurized storage device (72) through a closed-loop regulator that compares the pressure in the first side of electrolyzer with the pressure in the storage device.    DESCRIPTION OF DRAWING(S) - The figure is a schematic diagram of the inventive electrolyzer system.    Electrolyzer (22)    Interior cavity of pressure vessel (24)    Pressure vessel (26)    Cells (28)    Anode flow path (30)    Cathode flow path (32)    Power source (34)    Pressurized water source (36)    Level sensor (46)    Pressure sensor (48)    Water recirculation pump (50)    Separator (68)    Pressurized storage device (72)    Pressure regulator (74)