Castor, com and linseed oils with the addition of inhibitors were investigated using a DSC equipped with a pressure DSC cell. The inhibitors used in the experiments were 2,6-di-t-butyl-4-methylphenol and propyl gallate. The measurements were carried out under isothermal conditions in an atmosphere of oxygen. Thermal curves from DSC runs permitted the determination of onset and maximum points of the peak which were then compared to those of the pure oils. The apparent activation energies of oxidation of the oils were calculated using the model of the autocatalytic reaction and the Arrhenius equation.