Bio-oil was upgraded using supercritical 1-butanol over a Ru/C heterogeneous catalyst. The results clearly demonstrated that the use of a supercritical solvent resulted in an upgraded product with improved properties compared to upgraded bio-oil using no solvent or subcritical solvent conditions. These improvements included a decrease in oxygen content from 24.9 or 21.4 to 14.5% and an increase in the high heating value (HHV) from 27.9 or 30.5 to 32.0 MJ kg(-1). The most important improvement is that carbon deposition was limited to only 0.2% through the use of a supercritical solvent compared to 9.9% without a solvent. Thus, coking was overcome effectively during the upgrading process. The solvent played several roles: in addition to being the reaction medium and reactant, the solvent facilitated hydrogen dissolution, protected the catalyst, and enhanced the product properties. The reaction pathways in supercritical bio-oil upgrading primarily include esterification, etherification, acetalization, hydrogenation, and hydrodeoxygenation. In this study, the properties of upgraded bio-oil purified via vacuum distillation to remove the solvent were quantified.