Tests have been run on machinable hardness helical gears to study the influence of changes in calculated oil film thickness in the operating gear teeth in regard to the onset of surface pitting. Control tests were run at constant load to develop typical pitting patterns on the gear teeth within a reasonable test period. Subsequent tests were carried out to evaluate the changes in resistance to pitting that occurred when the oil film thickness was varied. All the tests were operated with an ample controlled supply of a petroleum-based lubricant@ symbol 2190 TEP@ that meets the specifications of MIL-L-1 7331.