Aviation lubricants were extensively tested at severe conditions to determine the performance advantages of incorporating a load carrying additive. A high load oil performed at least as well or better than a normal load oil in the bearing rig test at Type 1 through Type 2-1/2 conditions. At the extremely severe Type 2-3/4 conditions, in an inerted atmosphere, all oils tested containing load carrying additives successfully completed the 100-hour test, while all oils tested without the additive suffered catastrophic failure in less than 10 hours. The role of the load earring additive in the protection of loaded, moving parts, as in the Ryder Gear Machine, was examined. Data for the anti-scuffing protection afforded by this additive through surface adsorption on working gears is presented.