This paper discusses piston ring wear data obtained from operating a single cylinder internal-combustion engine fitted with an irradiated standard chromium plated top compression ring. A brief description of the engine equipment, the constantly-monitored lubricating oil flow system, the dual-channel gamma spectrometer and an outline of test method are included. The author stresses the development of a technique which permits a separate simultaneous record of the wear occurring on the face and on the side of the radioactive piston ring. Results are presented from constant speed engine operation with a series of different lubricating oil additive formulations.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Toronto, Canada, October, 1957.