This study investigated the influence of temperature and residence time on liquefaction of rice straw in subcritical CO2-subcritical water (subCO(2)-subH(2)O) and in subcritical CO2-supercritical ethanol (subCO(2)-scEtOH), considering the final reaction temperatures (270-345 degrees C) and residence times (15 and 30 min). Residence time was identified as a crucial parameter in the subCO(2)-subH(2)O liquefaction, whereas residence time had a marginal influence on subCO(2)-scEtOH liquefaction. When reaction conditions were 320 degrees C and 15 min, solvents have weak impact on the quality of bio-oil, HHV 28.57 MJ/kg and 28.62 MJ/kg, respectively. There was an obvious difference between the subCO(2)-subH(2)O and subCO(2)-scEtOH liquefaction mechanisms. In subCO(2)-subH(2)O, CO2 promoted the carbonyl reaction. In subCO(2)-scEtOH, supercritical ethanol have the function of donating hydrogen and promoting the reaction of hydroxyl-alkylation. (C) 2017 Elsevier Ltd. All rights reserved.