(57) Disclosed is a method for enhancing the conversion of carbonous materials, such as coal and oil shale. The method comprises converting the carbonous material in the presence of a vapor phase hydrogen donor material containing one or more hydrogen donor solvents wherein each donor material is characterized by: (a) a heterocyclic ring in which the heteroatom is nitrogen, (b) having at least one donatable hydrogen located on the heterocyclic ring, and (c) becoming more unsaturated and/or aromatic upon the loss of the donatable hydrogen(s). The conversion is performed at substantially atmospheric pressure, at an effective vapor residence time and at a temperature from about the boiling point of the hydrogen donor material to about 550°C.