When picking out the right lawn mower oil, it's important to check your owner's manual to see what the maker suggests.
There are, however, some general rules you can follow if you don't have the instructions handy.
A good motor oil that is detergent-based and has a viscosity value of 10W-30 or 5W-30 works best for most lawn mowers.
These oils are made to be very good at lubricating and protecting against wear and tear. They can also be used in both warm and cold conditions.
You might want to use a different viscosity oil if you live in a place with very high or very low temperatures.
For instance, a lighter oil like 10W-30 might be better in places that are very hot, while a thicker oil like 5W-30 or even 10W-40 might be better in places that are cold.
This is also important: make sure the oil you use is the right service rating for the engine in your lawn mower.
These days, most lawn mowers need oil that has an API service rating of SJ, SL, or SM.
If you use a high-quality oil that meets these requirements, your lawn mower will work better and last longer.