Two types of Malaysian oil palm biomass; namely Empty Fruit Bunch (EFB) and Palm Kernel Shell (PKS) are liquefied using sub-and supercritical water to produce bio-oil. Effects of temperatures (360, 390 and 450 °C) and pressures (25, 30 and 35 MPa) of the liquefaction of biomass on the bio-oil yields are investigated. The optimum liquefaction conditions for EFB and PKS using water are at supercritical conditions. PKS which consists of higher lignin content yields maximum bio-oil of about 41.3 wt % at temperature of 450 °C and the bio-oil yield from EFB is about 37.4 wt % at temperature of 390 °C.