Supercritical fluid extraction (SFE) is a separation technology that uses supercritical fluid solvent. Hydrogen can be produced from biomass via two thermochemical processes: (1) gasification followed by reforming of the syngas, and (2) fast pyrolysis followed by reforming of the carbohydrate fraction of the bio-oil. In each process, the water-gas shift is used to convert the reformed gas into hydrogen, and pressure swing adsorption is used to purify the product. In comparison with other biomass thermochemical gasification such as air gasification or steam gasification, the supercritical water gasification can deal directly with the wet biomass without drying and have high gasification efficiency in lower temperatures. The cost of hydrogen production from supercritical water gasification of wet biomass was several times higher than the current price of hydrogen from steam methane reforming. Biomass was gasified in supercritical water at a series of temperatures and pressures during different resident times to form a product gas composed of H-2, CO2, CO, CH4, and a small amount of C2H4 and C2H6.