The oxidation stability of biodiesels obtained from the transesterification of sunflower and soybean refined oils was studied using a method of accelerated oxidation (under 700 kPa oxygen atmosphere), the so-called PetrOXY method. The antioxidant Ionol BF 200 was used in a concentration range from 0 to 5000 ppm, and the experiments were carried out with temperatures varying from 130 to 145 degrees C. Oxidation kinetics could be described with a good precision, considering that correlation coefficients were above 0.99, obeying a first-order reaction kinetics in relation to the concentration of antioxidant for soybean biodiesel and an apparently zero-order kinetics for sunflower biodiesel (which was the result of mathematical approximations derived from a more chemically appropriated first-order kinetics). Reaction specific velocities were determined and enthalpies of activation for antioxidant oxidation were determined from Arrhenius plots. All the results indicated that, for the same inhibitor concentration, sun-flower-derived biodiesel was less stable towards oxidation than the soybean one. (C) 2013 Elsevier Ltd. All rights reserved.