Like so many things we Americans get bitched at for saying, it’s because that’s what the Brits used to call it.

A British man named John Cassell sold a brand of petroleum-based fuel trademarked as Cazeline. This eventually became Gazeline and then genericized as gasoline, shortened to “gas.”

One could ask why only “gasoline” is called “petrol” elsewhere in the world when several other fuels such as kerosene and diesel are also petroleum-based. Why isn’t diesel also called “petrol?”