Wet biomass and organic wastes can be efficiently gasified under hydrothermal conditions to produce a hydrogen rich fuel gas. New experiments in two tubular flow reactors and in two batch autoclaves with carbohydrates, with aromatic compounds, with glycine as a model compound for proteins and with real biomass are reported for different residence times, temperatures and pressures. It was found that at 600 degrees C and 250 bar all compounds are completely gasified by addition of KOH or K2CO3, forming a H-2 rich gas containing CO2 as the main carbon compound. Concentrations of CO, CH4 and C-2-C-4 hydrocarbons are low in the product gas (<1, similar to 3 and <1 vol%, respectively). Carbon balances for the smaller flow reactor are closed to better than 96%. Ranges of product concentrations are given as estimated from experimental reproducibility. Some reflections for the engineering of a pilot plant are presented. (C) 2000 Elsevier Science B.V. All rights reserved.