A number of factors determine the type of oil you should use in your lawn mower.
The most important thing is to select the right viscosity (the state of
Two basic viscosities are used for lawn mower engines – SAE 30 is your choice for mowing during times of warm weather, and 10W-30 is your choice for cold weather.
SAE (Society of Automotive Engineers) 30 is a single grade oil that is traditionally chosen to use in smaller air-cooled engines like those used in lawnmowers, tractors, and chainsaws. SAE 10W-30 oil is a single grade oil that can be used at lower temperatures (the W stands for Winter).
Two Stroke Oil
If your mower has a two-stroke engine (an internal combustion engine that completes one power cycle with two up-and-down movements of a piston during one crankshaft revolution), you’ll need to use a combination of gasoline with two-stroke oil.
What type of engine your lawnmower has should be listed in the manual and in all manufacturer instructions.
- You can’t use regular automotive oil for a lawn mower that has a two-stroke engine – the detergents and additives in automotive oil aren’t healthy.
Choose two-stroke oil that is labeled SF, SG, SH, and SJ (these are all performance ratings assigned by the API (American Petroleum Institute).
Generic Or Name Brand?
All the top lawn mower brands will push their brand of oil, but you don’t have to buy one specific brand. You can use a generic oil that has been specially formulated to use in lawn mowers and will benefit from lower prices for the same quality of oil.
What About Oil Additives?
There are a plethora of oil additive bottles on the shelves of automotive stores, but don’t give in to the temptation to add them to lawnmower fuel. Lawnmowers have small engines, and additives are only useful for large engines.
But, you should consider using a gas additive if the gas you are putting into your small engine has ethanol. 
Can You Use A Synthetic Lawnmower Oil?
The short answer is yes, you can.
In fact, synthetic SAE 5W-30 works best in both extremely cold temperatures (down to -20º F) and extremely hot temperatures (up to 120º F). SAE 5W-30 will provide better starting and will consume less oil in the long run.
Don’t Want To Deal With Oil?
If you don’t want to deal with oil, think about buying either an electric or cordless mower. They don’t need their oil changed – ever…which is a real selling point to some people and better for the environment.