In the present work, new pitches were obtained by supercritical extraction of Moroccan oil shales with water-shale oil as solvent. The aim of the research was to obtain pitches with very significant maturation degree of the organic matter. The evolution of the pitch Structure was studied through indexes calculated from quantitative infrared spectroscopy. The classification of the pitches enabled us to assess their degree of maturation. This allowed us to establish the water-shale oil mixture composition likely to give the best maturation of the oil shale's organic matter. (C) 2008 Elsevier B.V. All rights reserved.