The catalyst-free transesterification of castor oil under supercritical conditions, using methanol, was studied in this research to determine the molar ratio (methanol:castor oil) and reaction time that produced the biodiesel with the highest conversion by using a 10 L stainless steel batch reactor. The experiments were carried out with 30:1, 40:1, 50:1 and 60:1 molar ratios and reaction times of 5 min, 15 min, 25 min and 35 min under the critical temperature and pressure values according to the molar ratio tested. The reaction conversion was monitored by H-1 NMR spectroscopy. The biodiesel was characterized in order to evaluate its accordance to the ASTM D6751 specification and to plot the thermogravimetric and calorimetric profiles of the biodiesel with the highest conversion obtained by TGA and DSC analysis. A regression model was obtained as a reference to calculate the conversion under the studied range of molar ratios and reaction times in future experiments with a coefficient of determination of 95,22% and a standard error of +/-1,37% from the observed conversion. (C) 2017 Elsevier Ltd. All rights reserved.