In this study, different seaweed species were gasified in supercritical water as biomass feedstock. The experimental conditions were 500 degrees C of temperature and 1 h of reaction time. The amount of gases, the gas compositions and the amount of water soluble compounds from gasification were determined. The coke yields were found to be significantly lower than those obtained with lignocellulosic and protein contained wastes. The gaseous species detected contain mainly hydrogen, methane and carbon dioxide. The hydrogen yields ranging between 11.8 and 16g H(2)/kg seaweed have been obtained. On the other hand, the methane yields were found to be in the range of 39 and 104g CH(4)/kg seaweed. The contents of aqueous phases were also determined using various analytical techniques. DOC (dissolved organic carbon) values of aqueous phases showed the high extent of gasification. (C) 2011 Elsevier B.V. All rights reserved.