Biomass may be converted to more useful fuel and chemicals via thermo-chemical decomposition and biological digestion. Thermochemical conversion processes include three sub-categories: pyrolysis, gasification, and direct liquefaction. Two biomass conversion processes using water have been studied: hydrothermal up grading under subcritical water and supercritical water gasification in supercritical water conditions. The hydrothermal upgrading or direct liquefaction is a promising technology to treat waste streams from various sources and produce valuable bio-products such as biocrudes.