Straight off the bat, the answer is it depends on the engine of your lawn mower.
Lawn mowers can either have 2 stroke engine or a 4-stroke engine. Each uses a different gasoline formula. One can tolerate mixed gas just fine, and one will be damaged. One can use normal gasoline, and one cannot.
With your engine off for safety, locate the fuel tank and check how many intake ports there are. If there is only 1 port for oil and gas, then it's a 2 stroke engine. Otherwise, if there are two ports, it's a 4 stroke engine.
Other ways to tell is through the noise and gas emission of your mower while it's running.
If the sound of your engine is thunderous, then it is a 2-stroke engine. Otherwise, it's a 4 stroke engine.
If your mower exhausts a lot of gases, then it is 2-stroke. Otherwise, it's a 4 stroke engine.
As you can probably tell, 4-stroke engines are more environmentally friendly.
If you checked and you confirmed that you have a 2 stroke engine, you can safely use mixed gas, and your unit will be fine. Mixed gas only has a small amount of oil that is formulated to burn up as used along with the gasoline. It also doesn't leave any deposits behind. So, you can use it on a 2 stroke engine without any problems.
However, you should never use mixed gas in a 4-stroke engine. For this engine, fuel and oil must be added to the two ports separately.
Fresh unleaded gasoline with an octane rating of 87 or higher is required for most 4-stroke engines. Though it's not recommended, gas with ethanol (no more than 10 percent ethanol) can also be used.
To make the 2-stroke gas/ mixed gas more compatible with a 4-stroke engine, you can add high-quality two-cycle engine oil.
Mixed gas can clog your 4-stroke engine, and that clog can cause it to overheat.
Using a two-stroke fuel or mixed gas in a 4-stroke engine will cause oil smoke from the exhaust.
Adding oil in your 4-stroke engine fuel will create more wear and tear on the cylinder liner and piston and damage to the piston.
If you used mixed gas once or twice, it will likely not cause too much damage to your 4-stroke engine.
However, continued use will cause irreversible damage to your engine.
What you can do is simply drain the mixed gas from your mower and replace it with the proper fuel for a 4-stroke engine.
Two strokes need more oil than four strokes. Running a 2 stroke engine without enough oil can damage the engine. The oil keeps the pistons and cylinders lubricated. Without oil, the metals can melt and grate against each other, ultimately being permanently distorted.
Gasoline evaporates quickly, but oil doesn't evaporate.
You can test this by putting a drop of your gasoline on a piece of paper.
Wait a while and let the gasoline evaporate.
If the paper dries out completely, the gasoline is regular gasoline.
If there is still some oil left on the paper, the gasoline was is a gasoline blend or mixed gasoline.
Oil is used to prevent friction and wear in 2-stroke engines. Two-stroke engines require oil mixed into the gasoline to provide lubrication, yet 4 stroke gas doesn't have oil in it since 4 stroke engines have separate oil in the crankcase.
Using 4 stroke gas without oil can cause permanent damage to a 2-stroke engine.
Just like living creatures, machines need the right sustenance based on their system for them to work properly.
So, knowing the type of engine you have and what type of gas for lawn mowers is needed for it is crucial for optimum performance and prevention of damage.
So, now you know the different type of gas and their usage in lawn mowers, you can get both optimum performance and prevention of damage - the best of both worlds!