NOVELTY - Treating organic matter to convert it into a product involves contacting the organic matter with supercritical liquid where it reacts to form the product. The liquid may be heated by an external heating medium or internally by co-feeding an oxidizing agent with the liquid. The amount of the agent is predetermined to control the extent to which the reaction mixture is heated.    USE - For treating the organic matter e.g. lignite or brown coal, lignin, cellulose, hemicellulose, organic waste, plastic or generic polymer and converting it into a chemically decomposed product e.g. fuel, liquid phase of petroleum products such as substituted aromatics, diesel oil, asphaltenes, pre-asphaltenes, solid residue of char and gas of methane, hydrogen, carbon monoxide and carbon dioxide (claimed).    ADVANTAGE - The process provides sufficient activation energy for the reaction to occur with sufficient speed and for the liquid to attain characteristics sufficient to aid the process reactions; and for controlling chemical decomposition of organic matter. When followed by collection of the decomposition products and a separation, the separated products can collectively be of higher value than the unprocessed organic matter, and can be suitable for specific end uses. The process effectively treats wet organic solids without the need to pre-dry the solid. The organic solid can simply be milled and slurried and then processed by contact with the supercritical liquid. The process is applied to many types of organic matter having different moisture contents and chemical compositions. The use of supercritical water (greater than 220 bar and greater than 350 degrees C and less than 420 degrees C) in the reactor converts the lignite into smaller molecules that resemble heavy petroleum fractions, commonly referred to as oil, asphaltenes and pre-asphaltenes, and also yielding residual char, gas (mostly carbon dioxide) and produces water as the main products. In this way, lignite mined in its naturally wet state can be processed and used without a pre-drying step. There is no need for a high-pressure pump because the column of water in the shaft supplies the pressure. There is a lower operating cost because of the lower pumping costs and a high degree of safety compared with the use of high pressure equipment at the ground surface. The reactor and heat exchanger is made into a module which is lowered into a deep-sea trench from a ship. The module is built relatively cheaply from low-pressure equipment because the sea depth would provide a counter pressure. Another advantage of an undersea option is the use of ceramics for the reactor body itself, instead of stainless steel.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for an apparatus for treating organic matter arranged to convert the organic matter into a product upon contact with a supercritical liquid comprising an oxidizing agent introduction device for introducing a source of oxygen into contact with the organic matter; and a reactor. The reactor comprises a reaction zone in which chemical decomposition of the organic matter to form the product occurs, and the reaction zone is arranged for in use containment of the supercritical liquid.