A kinetic study in free catalyst transesterification of rapeseed oil was made in subcritical and supercritical methanol under different reaction conditions of temperatures and reaction times. Runs were made in a bath-type reaction vessel ranging from 200 degreesC in subcritical temperature to 500 degreesC at supercritical state with different molar ratios of methanol to rapeseed oil to determine rate constants by employing a simple method. As a result, the conversion rate of rapeseed oil to its methyl esters was found to increase dramatically in the supercritical state, and reaction temperature of 350 degreesC was considered as the best condition, with the molar ratio of methanol in rapeseed oil being 42. (C) 2001 Elsevier Science Ltd. All rights reserved.