We investigated the esterification of oleic acid with excess ethanol at sub- and supercritical reaction conditions (based on ethanol). This reaction can be used to make fatty acid ethyl esters, which are components of biodiesel fuel. The esterification proceeds smoothly with no added catalyst even at subcritical temperatures and pressures, which indicates that the more severe supercritical conditions are not required. Moreover, the reaction does not require a large excess of alcohol, and it can tolerate the presence of modest amounts of water in the feed stream. For the first time, the kinetics of noncatalytic ethyl esterification were determined. We report the forward and reverse rate constants at five different temperatures and the corresponding Arrhenius parameters. (C) 2010 Elsevier By. All rights reserved.