Acid catalyzed reactions of 1-octene on TiO2 in sub- and supercritical water were investigated (T= 250-450 degrees C, P=11-33 MPa). The main products were 2-octene and 2-octanol. Additionally, other liner C-8 alkenes and liner secondary C-8 alcohols were produced as by-products. Through kinetic analysis, acid catalyzed reactions can divide into the reaction catalyzed by Lewis acidic sites on TiO2 and the reaction catalyzed by protons produced by the dissociation of water molecules. Each type of the reaction is affected by water density or ionic product of water, respectively, therefore, reaction mechanism changes with temperature and pressure. From the contribution of each reaction type, the temperature dependence of cis/trans ratio of produced 2-octene could also be explained. (C) 2010 Elsevier B.V. All rights reserved.