Upgrading of Estonian shale oil - changing the chemical composition and correcting the boiling range - was effected by hydrogenation in an autoclave at 370 degrees C using a Co-Mo catalyst. Refined oil which yield reached 93 % is rich in different aliphatic, alicyclic and aromatic hydrocarbons and contains considerably less high-polar heterocompounds and alkanones as compared with unupgraded oil. Nevertheless, compound groups similar to those present in initial oil and, mainly, same individual components were identified in the composition of upgraded oil, the content of the groups as well as of single components in groups being strongly different. As a result of moderate hydrogenation, the chemical composition of Estonian shale oil becomes closer to that of natural crude oil, enabling to widen essentially the possible fields of use of shale oil.