[KenL]

I'd give it away as an incentive.

Imagine you went a restaurant where as you ate, the valet not only parked your car, but filled it with ... for free. A 15 gallon fill-up would only cost 90¢, plus valet time. Bring on the carne mechada.

That, or something to do with cheap explosions.

[joonix]

But if gas was widely available at 90c per tank, it wouldn't be a big deal. People don't flock to restaurants now because they give free tap water.

[KenL]

True, but there'd be a window where it was nice perk.

The first businesses to offer "free wifi!" or unlimited miles on a rental car had a first-mover advantage.