Four turbine oils formulated with varying types and concentrations of antioxidants were aged via D 943 exposure and examined extensively at 1000, 2000, 5000, and 10 000 h. Acid number, Rotary Pressure Vessel Oxidation Test (RPVOT), High Pressure Differential Scanning Calorimetry (HPDSC)RP, and sludge determinations were made at each time interval. Only a combined evaluation of the test results for the 10 000 h oil samples (a “Total Oxidation Products” approach) gave a reasonable estimation of the true oxidative state of the fluids. One shorter term test, ASTM D 6514, was found to give a fair prediction of the overall quality of the fluids at 10 000 h.