The oxidative stability of formulated lubricating oils, and virgin and re-refined lubricating base stocks, have been determined by high pressure differential scanning calorimetry. At pressures of 0.7 - 3.4 MPa (100-500) psig) air or O2 and temperatures near 200°C, degradation occurs with an appreciable generation of heat. Experiments have been conducted in both temperature programmed and isothermal modes. These data have been compared with multicylinder engine sequence test (III-C) results. Sensitivity to effects caused by a NOX environment, traces of olefinic materials added in the oil and the nature of metal surfaces have been demonstrated. Data on the response of re-refined and virgin base stocks to fixed quantities of an additive have been obtained. They are indicative of the wide diversity of the substances in question. The results of these studied indicate that the induction period measurements yield important information on the response of base stocks to additive treatment which could be used in quality control for formulating lubricating oils. Further studies are, however, needed to obtain more definite conclusions.