An instrument to evaluate grease or ball bearing performance at high temperatures under actual operating conditions has been developed. Operation of the bearing in an oxygen atmosphere has considerably reduced the total testing time required. By measuring the rate of oxygen consumption during a test, data on the chemical changes taking place in the grease are obtained, and the time of grease failure can be pinpointed quite accurately and reproducibly. Typical oxygen consumption curves of various greases, as well as data which show the effect of the internal bearing clearance and the bearing's ABEC classification on grease life, are included. Contributed by the ASLE Technical Committee on Bearings and Bearing Lubrication and presented at the Annual Meeting of the American Society of Lubrication Engineers held in Detroit, Michigan, April 1957.