Upgrading of solid fuels

In a process for the hydrothermal treatment of a low rank solid fuel in the presence of added hydrogen the improved method of reducing hydrogen consumption which comprises forming a mixture of particulate low rank solid fuel and water, heating the mixture in an inert atmosphere to a temperature between about 300.degree. and 700.degree. F. at a pressure sufficient to maintain the water liquid in the heating zone, venting the heating zone to release the generated gases and then subjecting the mixture to hydrothermal treatment at a temperature between about 300.degree. and 700.degree. F. and a pressure sufficient to maintain the water liquid in the hydrothermal zone in the presence of added hydrogen.