This study examined the effect of glycerol used as a co-solvent on yields of bio-oil derived from rice straw through hydrothermal liquefaction (HTL). The reaction was conducted in a high-pressure batch reactor with different volume ratios of glycerol to water. The quality of the derived bio-oil was analyzed in terms of its elemental composition, heating value, water content, ash content, and acid number. Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry were conducted to analyze the chemical composition of the derived bio-oils. The following optimal conditions were obtained: 1:1 vol ratio of glycerol to water with 5 wt% of Na2CO3 at 260 degrees C for 1 h. Under these conditions, 50.31 wt% of bio-oil and 26.65 wt% of solid residue were produced. Therefore, glycerol can be used as a co-solvent in HTL of rice straw at moderate temperatures to obtain bio-oil with high yield and quality. (C) 2016 Elsevier Ltd. All rights reserved.