Kukersite oil shale + pine bark, kukersite oil shale + peat as well as kukersite, bark and peat individually were submitted to thermochemical liquefaction in an autoclave with and without solvent for two hours at different temperatures from 340 to 420 degrees C. Water and benzene as solvents were used. The influence of several factors such as temperature, solvent and its type, and oil shale-to-peat or oil shale-to-biomass ratio on the yield of liquid, gaseous and solid products was investigated. The chemical composition of the goal liquid product separated as the benzene soluble oil was characterised by using FTIR-spectroscopy and ultimate analysis apparatus. Group composition of the oil was determined by using thin-layer chromatography. In co-liquefaction experiments several synergistic effects in product yields were observed. The most important synergistic effect was noticed at co-liquefaction of the mixture oil shale with peat (10 : 4 by mass of the organic matter) at 360 degrees C in the medium of water in which case the yield of the liquid product was 25% higher than the sum of corresponding yields obtained at liquefaction of oil shale and peat separately in the same experimental conditions. The group composition of oils shows that various polar and high-polar oxygen compounds prevail over hydrocarbon fractions. Data on the elemental and group composition demonstrate that partial substitution of biomass or peat for oil shale leads to obtaining chemically modified shale oil.