Cellulose, a major component of biomass, was gasified in hot-compressed water using a reduced nickel catalyst at different reaction temperatures from 200 degrees C to 350 degrees C. The reaction mixture was separated to gases, oil, char and water-soluble products to discuss reaction mechanism based on the product distribution. The water-soluble products were considered as intermediates, and the obtained hydrogen was consumed by methanation reaction. The following simplified reaction scheme was proposed : [GRAPHICS] The effect of supports was also examined. Supports showed the strong effect on the gas yield, and the catalytic activity depended on the overall catalyst size rather than the surface area.