Methyl and ethyl esters as biodiesel fuels were prepared from linseed oil with transesterification reaction in non-catalytic supercritical fluids conditions. Biodiesel fuel is a renewable substitute fuel for petroleum diesel fuel made from vegetable or animal fats. Biodiesel fuel has better properties than that of petroleum diesel fuel such as renewable, biodegradable, non-toxic, and essentially free of sulfur and aromatics. The purpose of the transesterification process is to lower the viscosity of the oil. The viscosity values of linseed oil methyl and ethyl esters highly decreases after transesterification process. The viscosity values of vegetable oils vary between 27.2 and 53.6 mm(2) s(-1), whereas those of vegetable oil methyl esters between 3.59 and 4.63 mm(2)s(-1). Compared with no. 2 diesel fuel, all of the vegetable oil methyl esters were slightly viscous. The flash point values of vegetable oil methyl esters are highly lower than those of vegetable oils. The transesterification of linseed oil in supercritical fluids such as methanol and ethanol has proved to be the most promising process. Methanol is the commonly used alcohol in this process, due in part to its low cost. Methyl esters of vegetable oils have several outstanding advantages among other new-renewable and clean engine fuel alternatives. The most important variables affecting the methyl ester yield during the transesterification reaction are molar ratio of alcohol to vegetable oil and reaction temperature. Biodiesel has become more attractive recently because of its environmental benefits. Biodiesel is an environmentally friendly fuel that can be used in any diesel engine without modification. (C) 2008 Elsevier Ltd. All rights reserved.