Studies have been conducted for determining the distribution of the lubricant in a crankcase scavenged two-stroke cycle engine. Presently, it is not obvious how newly supplied oil reaches each engine part and how it leaves the engine through the exhaust gas. Furthermore, it is desirable to know what percent of the supplied oil is exhausted during the scavenging period and what percent is burned in the combustion chamber with the gasoline.Three different lubrication systems were studied utilizing radioisotopes: premixed fuel and oil; manifold supply system for the oil; and crankcase supply system for the oil. The lubricating oil was tagged with tritium. The lubricating oil behavior in the crankcase scavenged two-stroke engine has been investigated within the limited operating condition of these tests. The tests show that almost all supplied oil was exhausted within one hour, and the remainder was exhausted gradually.With the premixed supply system, the oil supplied to the engine is exhausted through the exhaust system more rapidly than when the separate lubrication supply system is used. Thus, in the separate supply systems-the manifold supply and crankcase supply systems-the amount of oil remaining in the engine is greater and the residence time longer than that of the premixed supply system for the same engine operating conditions. Consequently, superior lubrication characteristics can be expected with the separate lubrication systems for crankcase scavenged two-stroke cycle engines.