Cutaway of prototype "hybrid air" car. Image: PSA Peugeot Citroen

Tell us if you share this frustration. You pull into a gas station, hand over your life savings, fill the tank and - and for what? With gas in the United States averaging $3.31 per gallon this week and the average car getting about 27 mpg in regular driving, you'll just have to hand your life savings over again when you refill next week.

Some gas-electric hybrids can do better than 50 mpg, but not a lot of people own them. Though you spend less on gas, you generally spend more up front on the price of the car. Their batteries are heavy and expensive.

But what if someone offered you a car that could get up to 117 mpg in city driving? A car that would cost about $1,500 less than typical hybrids? It need not look like some pod from a Lady Gaga concert. When it's not running on gasoline, it uses … the air. There would be a sturdy tank of compressed air in the floor or trunk, recharged by the engine or the brakes.

Peugeot Citroen, the French automaker, has now shown off a prototype for such a system and claims on its website (in French) that it could start selling air-hybrid cars in Europe by 2016. The company, according to European news reports, says that on local streets, the cars would mostly run on compressed air, cutting gasoline use - and costs - by as much as 80 percent. The technology would start in existing subcompact models, the company said, but soon expand to include vehicles of all sizes.

" We are not talking about weird and wacky machines," a company spokesman was quoted as saying. "These are going to be in everyday cars."

Peugeot Citroen says it took on "the challenge of creating an environmentally friendly vehicle," and expects it would also save its customers money. It got some backing from the French government, which, like the U.S. government, is pushing automakers to get better fuel efficiency.

But will it be viable? Peugeot and Citroen, which joined forces in the 1970s, both pulled out of the U.S. market decades ago, and have been losing market share in Europe. It's important for them to look innovative.

So are they on to something big? Or is it just one more concept car that you will never see on the road?