The kinetic features of auto- and initiated oxidation of four basestock specimens of hydraulic oils at 120, 130, and 140degreesC were studied. The key reactions in the mechanism of the oxidation of each sample were identified, and the magnitudes of the corresponding kinetic parameters and their activation energies were determined. The kinetic models derived quantitatively describe the oxygen uptake and hydroperoxide buildup curves measured in the oxidation of these base oil specimens. The kinetic parameters were calculated and the oxidizabilities were compared for two specimens at 70degreesC, the accelerated oil-test temperature. The results of the prediction were analyzed, and the reasons for the change in the relative oxidizability of hydraulic-oil basestocks with a decrease in temperature were established.