The fuel mixture for a chainsaw includes gasoline and oil. Chainsaws use two-stroke engines that do not have the separate motor-oil reservoir of four-stroke engines. Most manufacturers require a fuel to oil ratio of 50:1.
Creating the 50:1 fuel mix requires adding approximately 2.5 ounces of oil to a gallon of gasoline. The procedure calls for adding the oil to half the gasoline and mixing before topping off the container. Manufacturers recommend using gasoline with an octane rating of 87 to 89 or higher in the fuel mix. The oil and gasoline tend to separate over time, so the user should shake the container before fueling the saw and avoid mixing more fuel than he can use in a few days.
Chainsaws burn the oil and gasoline while in operation. This results in more pollution than a similarly sized four-stroke engine produces. It increases the smoke in the engine exhaust.
Two-stroke engines operate in positions that stall four-stroke ones, making them ideal for use in chainsaws. They are lighter in weight and provide more power than their counterparts provide, which is another advantage with a saw. However, the dilution of the oil by the fuel increases the wear on the engine, and they do not last as long as a four-stroke engine.