ConclusionThis study showed that oil palm biomass can be successfullyliquefied using subcritical and supercritical water to obtain bio-oil.The hydrothermal liquefaction of EFB, PMF and PKS at supercriticalcondition of 390◦C and 25 MPa, which corresponds to the lowestdensity and dielectric constant of water explored in this study,produced maximum bio-oil yield of 37.39 wt%, 34.32 wt% and38.53 wt%, respectively. The differential thermogravimetric anal-ysis (DTG) of the biomass feedstocks provided important insightinto their thermal degradation behaviors. The lignocellulosic con-tent of the biomass influenced the yield of the bio-oil as well as thechemical compositions. It was found that the bio-oils produced atoptimum condition contained phenols and methoxy phenols as themajor components as a result of lignin degradation at high tem-perature of 390◦C. The feasibility of liquefying oil palm biomassfor bio-oil production using water as a green solvent as shown inthis study has opened up the possibility for further research anddevelopment into commercial and industrial scale.