In this study, hazelnut shell, sunflower seed shell and olive husk were subjected to supercritical fluid extraction (SFE) in an alkali medium using different solvents. The highest yield (99.1%) of SFE was obtained from sunflower seed shell with water solvent and 5/5 KOH alkali ratio run at 653 K of the fatty acids from SFEs, oleic acid was the major constituent (80.2 +/- 3.8%) followed by linoleic (67.7 +/- 3.2%) and palmitic (8.3 +/- 0.91%) acids. The most important fuel properties, such as proximate analysis, ultimate analysis and higher heating value of five oilseed shells were determined by standard testing methods. The carbon content of the selected shell species varies from about 47.4% to 53.5% due to varying lignin and extractives content. The hydrogen content of the species varies from 5.8% to 6.7%. The oxygen content ranges from 35.5% to 41.6%, and N ranges from 0.5% to 1.6%. The lignin content ranges from 17.0% to 52.3%. (C) 2002 Elsevier Science Ltd. All rights reserved.