What Gas Does My Small Engine Need?

It’s inevitable. You’re going to need to refuel your mower at some point each summer, maybe even a few times depending on the size of your yard! So make sure that when you head to the pump to fill up your gas can that you’re getting the right type of fuel for your mower and other outdoor gas-powered equipment. The wrong fuel type can do anything from affect the performance of the engine to even damage the engine and possibly void the warranty.

Your operator’s manual is always the best resource, but here’s a quick guide to help you navigate between the options and keep your engine running at its peak performance.

• Always add fresh, unleaded fuel with an E10 blend or less in your small engine. An E10 fuel is a blend of unleaded gasoline and up to 10 percent ethanol.
• Use a minimum of 87 octane/87 AKI (91 RON). See below for recommendations in high altitudes that are necessary to remain emissions compliant.
• Be sure to avoid high ethanol blends such as E15 or E85. These higher blends can corrode metal parts and degrade plastic components within small engines — which can cause poor engine starting and even engine failure. That’s why the use of E15 and E85 blends in small engines is prohibited by Federal Law.
• Canned fuel products such as Briggs & Stratton® Advanced Formula Ethanol-Free Fuel combines ethanol-free unleaded gasoline with a fuel stabilizer to prolong fuel life and are a great alternative to the pump for your small engine.

If you live in a high altitude area of over 5,000 feet (or 1524 meters):

• Use a minimum of 85 octane/85 AKI (89 RON). Without this high altitude adjustment, the performance will decrease and emissions and fuel consumption will increase. The adjustment helps avoid those effects and to remain emissions compliant.
• A high altitude kit or adjustment is not recommended for engine operation below 2,500 feet (762 meters).

Mixing Oil & Fuel

Some engines require a mix of oil and fuel to run properly. Always check your operator’s manual to know what type of engine powers your outdoor power equipment and if it’s an engine that requires a mix. In general,
• 4 Stroke Cycle Spark Ignited Engines: Do not mix oil in gasoline, or modify the engine to run on alternate fuels. Follow the guidelines above and your operator’s manual for the best fuel for the engine. Many of today’s lawnmowers use 4 Stroke Cycle Spark Ignited Engines.
• 2 Stroke Cycle Spark Ignited Engines: Many of today’s handheld outdoor power equipment use 2 Stroke Cycle Spark Ignited Engines. A common ratio is a of mix high quality, 2-cycle oil at a 50:1 gas to oil ratio. However, the ratio may vary depending on the product – so be sure to check what the specific ratio is for your equipment.

Fuel Storage


Did you know fuel can begin to go stale in just 30 days? Stale fuel can lead to gum and varnish which can clog an engine’s components. These clogs can lead to inconsistent starting, poor performance, or even engine failure. In addition, these traits associated with bad fuel void your engine’s warranty.

Improve your engine’s performance and life by adding an alcohol-free fuel treatment and stabilizer every time you buy fuel. We recommend Briggs & Stratton’s Advanced Formula Fuel Treatment and Stabilizer, which stabilizes fuel for up to three years. Regardless of the altitude, always remember, when filling up your can, add an effective fuel treatment!

One more very important tip: be safe when handling and storing fuel! All fuel and fuel vapors are extremely flammable and explosive and need to be handled with extreme care.

With these tips in mind, you’ll be running your mower with the best fuel all summer long so you can keep your mower and your lawn in great shape!

NOTICE: Customer service questions are not monitored via the blog. If you need assistance with your Briggs & Stratton engine or power equipment, please contact our Answer Center or post your question to our User Community.