Four bench tests, designed to evaluate thermal and oxidative properties of industrial gear oils, were used to study several additive packages.The following results were noted: (1) all the bench tests have some correlation with each other except for the panel appearance in the panel coker tests; (2) the P chem. of the additives affects the thermal stability of the oil and the depletion of the component with time; other controlling factors are of less importance, depending on the selection of the P component; and (3) the use of detergents and dispersants are effective in reducing sludge formation.