The marine brown alga, Sargassum patens C. Agardh, floating on the Yellow Sea, was collected and converted to bio-oil through hydrothermal liquefaction with a modified reactor. A maximum yield of 32.1 +/- 0.2 wt.% bio-oil was obtained after 15 min at 340 degrees C, at a feedstock concentration of 15 g biomass/150 ml water, without using a catalyst. The bio-oil had a heating value of 27.1 MJ/kg and contained water, lipid, alcohol, phenol, esters, ethers and aromatic compounds. The solid residue obtained had a high ash and oxygen content. The results suggest that S. patens C. Agardh has potential as biomass feedstock for fuel and chemical products. (C) 2011 Elsevier Ltd. All rights reserved.