This paper presents the studies on the liquefaction of three types of oil palm biomass; empty fruit bunch (EFB), palm mesocarp fiber (PMF) and palm kernel shell (PKS) using water at subcritical and supercritical conditions. The effect of temperature (330, 360, 390 degrees C) and pressure (25, 30, 35 MPa) on bio-oil yields were investigated in the liquefaction process using a Inconel batch reactor. The optimum liquefaction condition of the three types of biomass was found to be at supercritical condition of water i.e. at 390 degrees C and 25 MPa, with PKS yielding the maximum bio-oil yield of 38.53 wt%, followed by EFB and PMF, with optimum yields of 37.39 wt% and 34.32 wt%, respectively. The chemical compositions of the bio-oils produced at optimum condition were analyzed using GC-MS and phenolic compounds constituted the major portion of the bio-oils, with other minor compounds present such as alcohols, ketones, aromatic hydrocarbons and esters. (C) 2014 Elsevier B.V. All rights reserved.