Esterification of free fatty acids (FFA) with glycerol in supercritical carbon dioxide (SC-CO2) media to produce designer monoacylglycerols (MAG) for food, cosmetic, and pharmaceutical industries, was conducted to elucidate the reaction kinetics and provide the reaction mechanism. Reactions were conducted in SC-CO2 at 10-30 MPa, 170-250 degrees C in a batch stirred reactor using an anhydrous glycerol to oleic acid initial molar ratio (gly/oleic) of 10:1, 1:1 and 1:2 and in supercritical nitrogen at 10 MPa and 250 degrees C using 10:1 gly/oleic. Samples were collected as a function of time and MAG, diacylglycerol, triacylglycerol and FFA concentrations were determined using thin layer chromatography-flame ionization detection. The rate of MAG formation at 50% of equilibrium concentrations (Rate-50%) increased significantly (P <= 0.05) with temperature but was not affected by pressure or supercritical media(p > 0.05). Rate-50% values for 10: 1 and 1: 1 gly/oleic were similar (p > 0.05) but higher (p <= 0.05) than that for 1:2 gly/oleic. Equilibrium concentration of MAG significantly (p <= 0.05) decreased with decreased initial glycerol concentration. The calculated rate constants provided a better understanding of the mechanism and are essential for optimal process design. (c) 2007 Elsevier B.V. All rights reserved.