Two-stroke oil (also referred to as two-cycle oil, 2-cycle oil, 2T oil or 2-stroke oil) is an engine oil intended for use in two-stroke engines.
Unlike four-cycle engines which have a closed crankcase, these lightweight engines use the crankcase as part of the induction tract, and therefore, oil must be mixed with gasoline to be distributed throughout the engine for lubrication. The two-stroke oil is ultimately burned along with the fuel resulting in exhaust emissions with blue smoke and/or a distinctive odor.
The oil-base stock is either petroleum, vegetable, semi-synthetic or synthetic oil and is mixed with petrol/gasoline at a fuel-to-oil ratio ranging from 16:1 to as low as 100:1.
Engine original equipment manufacturers (OEMs) introduced pre-injection systems (sometimes known as "auto-lube") to engines to operate from a 32:1 to 100:1 ratio. Oils must meet or exceed the following typical specifications: TC-W3TM, NMMA, [API] TC, JASO FC, ISO-L-EGO.
Comparing regular lubricating oil with two-stroke oil, the relevant difference is that two-stroke oil must have a much lower ash content. This is required to minimize deposits that tend to form if ash is present in the oil which is burned in the engine's combustion chamber.