A fundamental study of the steam reforming of biogas and that derived from supercritical water gasification of glucose was conducted with a hydrogen-permeable palladium-silver membrane reactor. The hydrogen permeabilities for H-2-H2O (4:1), H-2-CO2 (4:1) and H-2-N-2 (4:1) mixtures from 573 to 673K were compared with those in the presence of hydrogen only. Water and nitrogen did not affect hydrogen permeability, whereas carbon dioxide tended to suppress its permeation in the high pressure region. Steam reforming of test gas 1 (moles H-2 : CH4 : CO2 = 50 : 10 : 40) and test gas 2 (moles H-2 : CH4 : CO2 = 10 : 40 : 50) mixtures having compositions expected from supercritical water gasification was carried out in the presence of 2 wt% Ru/Al2O3 at 723 K and pressures up to 0.5 MPa. Methanation was dominant and slightly decreased as hydrogen permeated through the membrane in the steam reforming of the hydrogen rich mixture (test gas 1), whereas there was almost no effect of the membrane reactor for methane rich mixture (test gas 2). A new system combined the supercritical water gasification system and steam reforming system was developed and gas formation from glucose was carried out at 673 K and 10 MPa for supercritical gasification and from 0.1 to 0.5 MPa of reaction pressure. The experiments changing the order of catalytic bed and Pd-Ag membrane in the membrane reactor for steam reforming revealed that the elevated high pressures and hydrogen removal before catalytic steam reforming are advantageous for high hydrogen recovery. (C) 2009 Published by Elsevier Ltd.