This paper integrates acidolysis and in situ hydrogenation of biomass to produce bio-oil featuring a high yield and also a high effective hydrogen/carbon molar ratio (H/C-eff). A catalytic amount of trifluoromethanesulfonic acid (HOTf) is found to be very effective to cleave glycosidic bonds in carbohydrates and beta-O-4 bonds in lignin, resulting in the formation of various carbohydrate/lignin-derived radicals. The in situ hydrogenation in the presence of Ru/C and H-2 stabilizes the resulting radicals and, thus, prevents their repolymerization. This HOTf Ru/C system is applicable to a wide range of feedstocks. Typically, the yield of bio-oil (dichloromethane extract) from pine wood at 160 degrees C can be as high as 43.2 wt % with a H/C-eff of 1.24, which is high enough to be co-processed in the existing refineries.