Historically, most cars have run on gasoline, but that doesn't have to be the case in the future: other liquid fuels and electricity can also power cars.
So what are the differences between these options?
And which one's best?
Gasoline is refined from crude oil, a fossil fuel extracted from deep underground.
The energy in gasoline comes from a class of molecules called hydrocarbons.
There are hundreds of different hydrocarbons in crude oil, and different ones are used to make gasoline and diesel — which is why you can't use them interchangeably.
Fuels derived from crude oil are extremely energy-dense, bringing a lot of bang for your buck.
Unfortunately, they have many drawbacks.
Oil spills cause environmental damage and cost billions of dollars to clean up.
Air pollution from burning fossil fuels like these kills 4.5 million people each year.
