A challenge for manufacturers is how to compress the gas into tanks small enough to fit in a compact car and yet still provide enough fuel for hundreds of miles of driving between refuelings.

Narrator: If you're not sure what kind of car this is ... which included plenty of drop tanks, or belly tanks. Belly tanks were supplemental gas tanks strapped to World War II fighter planes ...

Options for weight savings that automakers are investigating include installing things like plastic fuel tanks (PDF ... The chart below shows that for a small car with a 1.6-liter engine, reducing ...