Gasoline

[Dwight FitzSimons]

Premium gasoline has slightly less energy than regular gas. And, the oil refiners are required to include adequate additives in ALL gasoline to keep the engine clean and prevent emissions as far as possible. One should use high enough octane to prevent pinging (knock), but no higher, Any higher octane will be money wasted.
-Dwight

[NCDave51]

Well said here, and always a great topic to unravel.

Lots of good information - start with Wikipedia! - on the differences between research octane number (RON) and motor octane number (MON) and why that little label on your new car’s filler flap has both these numbers. Diesel engines use something similar: the cetane number.

And gas doesn’t truly have octane per se: isoheptane and isooctane are the markers the fuel companies use.