NOVELTY - The plant consists of an upper (12) and a lower (14) bath of molten metal: carbon-containing material is fed to the upper bath by a feed system (33). This bath also incorporates an outlet for liquid slag, an outlet for gases, recycle metal inlet and outlet passages for transfer of metal to and from the lower bath, and a pressure regulation system. The lower bath has recycle metal inlet and outlet, injectors (72,74) for oxygen and water, a synthesis gas outlet, and a pressure regulation system. One of the recycle ducts has an injector (30) for inert gases. The pressure in the two baths (preferably 25-3000 psig) is independently controlled by varying the amount of gases vented through their respective pressure regulation systems, and the molten metal flows between the baths by a combination of gravity and gas-lift. The pressure in the lower bath is used to control the amount of metal in this bath relative to that present in the upper bath.    USE - For gasification of carbon-containing materials to synthesis gas. Especially useful for gasification of coal or organic waste materials.    ADVANTAGE - Allows destruction of e.g. tires or hazardous organic wastes without pollution: produces sulfur-free synthesis gas from sulfur-containing coal. Produces a pure synthesis gas at high pressure. Does not use pumps etc. for transfer of molten metal.    DETAILED DESCRIPTION - The inner walls of the baths and the recycle ducts are heated, and the gases vented from the lower bath may be cooled in a heat exchanger forming part of the pressure regulation system. The lower bath recycle inlet and outlet may be at different levels in the bath, preferably with the inlet lower than the outlet. An ADDITIONAL CLAIM is included for a plant to convert a carbon-containing feed material to a gas containing hydrogen and carbon monoxide, including an upper bath operating at 1000 degrees C or more and a pressure of 0-15 psig, and a lower bath at 25-3000 psig. The level of metal in each bath is controlled by the pressure within the bath. Both baths are equipped with heat exchangers as part of their pressure regulating systems.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic cross-sectional side view of the gas production plant.    Upper molten metal bath (12)    lower molten metal bath (14)    gas lift injector (30)    feed system (33)    water inlet (72)    oxygen inlet (74)