ElI5, does filling up Supreme gas give you more milage then regular and is it significant?

Question

ElI5, does filling up Supreme gas give you more milage then regular and is it significant?

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Answer 1

In theory, it should make no difference**.

The difference between different fuel octanes is their resistance to pre-ignition. In short, a higher number means the engine can have compressive higher forces occurring, and the fuel will remain controllable (and not explode before you want it to).

A higher octane gas in an engine that doesn’t need it, shouldn’t change the fuel consumption.

**Only note is that lower grades typically have 10-15% ethanol, whereas the highest grade typically has 0%. Ethanol is less energy dense than gasoline, so mileage may increase with a higher octane **if** the car increases fuel usage to maintain the same power output.