Does premium gas burn slower than regular gas? Fuel Facts

By Sunoco Fuels
Apr 22, 2025 | Sunoco, Sponsored Content, Fuel Facts | Posted in News and Notes | From the May 2024 issue | Never miss an article

Photograph by Quentin Martinez

Something we’ve heard over the ages: High-octane fuel actually burns slower than regular-grade fuel. Is that true? Are we choosing the wrong pump? To find out what the science says, we asked an actual scientist.

Gasoline is made up of many different components, notes Zachary J. Santner, manager of Product Engineering and Business Optimization at Sunoco Performance Products. When lead was phased out of pump gasoline, to maintain octane levels, the industry turned to aromatic hydrocarbon compounds such as naphtha, toluene and ethyl-xylene.

By definition, these aromatics feature a ring structure at the molecular level. These compounds burn relatively slowly, Santner explains, due to the time required to break the bonds that create that ring structure.

Slower-burning fuels can be more likely to coke, leave deposits and produce soot. For an example, compare the relative cleanliness of propane (quick-burning, short-chain hydrocarbons) against diesel (slow-burning, long-chain hydrocarbons.)

Today’s pump fuels contain less aromatics than yesterday’s, he continues, as other compounds–like paraffins and ethanol–have become favorable for raising octane.

What about the level of aromatic compounds found in the fuel at your local pump today? As usual, Santner says, the exact amount can vary depending on several factors, including location, refinery and season.

Should you be concerned? Depends. If you’re running a highly stressed, large-bore engine–picture a Can-Am race car or a tractor set up for pulling competition–then yes, the speed that the flame front moves through the combustion chamber does matter. For these very specific applications, Sunoco offers SR18, a fast-burning, 118-octane fuel nearly free of aromatics. (It does use lead to make that much octane, though.)

For the rest of us, Santner continues, avoiding detonation and maintaining the correct air/fuel ratio are significantly more important. Don’t avoid high-octane fuels due to concerns of burn speed, he stresses.

And for those tuning at the ragged edge, he adds, Sunoco’s race fuels are always blended to a constant recipe. Unlike with street fuels, the mix doesn’t vary by location, refinery or season.

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Comments

mapleglen New Reader
4/24/25 11:59 a.m.

I taught high school Power Technology for 30 years. To get the kids into the grove, the first day assigment was to look up "octane" and what does it mean. 99% of them guessed and said "burns faster". Used to stand in front of them and pretend I was in a cylinder with exploding gas. Slaming a book on the table made a terrible noise and woke them up. Told them gas under compression does not burn like that, but starts slowly into a crescendo. It was fun till one day in the late 90s, a student read his homework with the perfect answer. I was really amazed and asked , where he found it. He said on the World the World Wide Webb. I said what? Things sure change fast.

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