Several multiviscosity grade oils were subjected to a special 240-hour endurance test procedure in an Army high-output two-cycle diesel engine, and certain of the oils were laboratory tested in the Army's multifuel, four-cycle compression ignition engine and in the Army's air-cooled four-cycle diesel tank engine. Certain of the lubricants were also subjected to standard hydraulic/power transmission tests because acceptable power transmission performance will now be a formal requirement in the D-revision to the engine lubricant specification MIL-L-2104. Parallel to these laboratory evaluations, pilot field tests were conducted in combat/tactical vehicles (engines and power shift transmissions) at three Army bases. The limited field tests indicated that the use of arctic/conventional multiviscosity grade lubricants at ambient temperatures up to 38°C(100°F) may be possible, and their introduction under MIL-L-2104 should be pursued. Laboratory test results produced a suitable two-cycle diesel engine lubricants qualification test, and showed that SAE grade oils are acceptable for use in Army diesel-powered combat/tactical engine and power transmission fluid systems. Areas for continued lubricant development are outlined.