Abstract: Methods are disclosed for reducing the nitrogen content of shale oil by selectively removing therefrom nitrogen-containing compounds. The nitrogen content of shale oil is reduced by a process comprising lowering the viscosity of the shale oil and then contacting the shale oil with a sufficient amount of a solvent which is selective toward the nitrogen-containing compounds present in the shale oil. The selective solvent is selected from the group consisting of organic acids, and substituted organic acids, particularly acetic, formic and trichloroacetic acids and mixtures thereof. The selective solvent system containing the nitrogen-containing compounds is separated from the reduced nitrogen content shale oil raffinate.