Narrator: : This is Science Today. The next time you fill your tank, remember that gasoline and diesel are not the only fuels out there. Engineer Jim Heffel of the University of California, Riverside led a team that created a truck that runs on hydrogen. It's a conventional truck, only slightly modified. Why hydrogen?

Heffel: It has a few benefits. One, that the main exhaust product's water. And secondly, it can be made from water, so it's a renewable fuel.

Narrator: : A non-polluting, renewable resource vehicle that can be built with existing technology? You'd think car companies would be rushing to make them -- but they're not.

Heffel: The drawback is, there's no hydrogen refueling stations. No one wants to build a hydrogen refueling station until there's cars, and no one wants to build cars until there's places to fill them up.

Narrator: : One way around that logjam is using hydrogen in fleet vehicles and buses. Then when people get used to the idea, says Heffel, consumers will start asking for their own hydrogenmobiles -- especially as petroleum runs out and gasoline prices rise. For Science Today, I'm Steve Tokar.