The average fuel economy for a new car in the United States is 25 m.p.g. That's far less than the 121 m.p.g.-equivalent of the Scion iQ EV, which is the most fuel-efficient passenger vehicle on the market.

But what if a car could get 200 miles per gallon?

That's what Volkswagen has achieved with its XL1 - a two-seater that will be the most fuel-efficient car to ever go into production when it makes its way down a German assembly line next year.

With a price tag of about $145,000, the return on investment, at current fuel prices, would take decades. Still, that's hardly the point. In the mad dash to the 54.5 m.p.g. corporate average fuel-economy standard the U.S. government has mandated by 2025, the XL1 shows it's more than possible using current technologies.

On the XL1, those technologies involve the extensive use of aerodynamics and lightweight materials, including a carbon-fiber body and magnesium wheels, as well as a power plant that combines all of the most fuel-efficient systems into one.

Not only does the XL1 use one of the smallest engines ever to be fitted inside a car; its 0.8-liter two-cylinder runs on diesel that is direct-injected, turbocharged, and enhanced with a 27-horsepower electric motor.

It's a triple threat of efficiency that will, unfortunately, be available only in Europe. Volkswagen is making just 250 XL1s, none of which will be headed to the United States because Department of Transportation safety standards would require too many modifications.

But for a few days in late November, Volkswagen made the car available for media test drives in the sprawling, rutted parking lot of the Hollywood Park racetrack in Inglewood, Calif.

What's most striking about the XL1 is its shape, which looks like something out of Futurama, with its teardrop profile and enclosed rear wheels - both of which were shaped to give the car the lowest coefficient of drag of any production car created to date, measuring just 0.19.

Getting inside is a matter of gliding through its gullwing doors. Doors that swing out, instead of up, wouldn't provide enough head clearance in a car so domed its ingress would otherwise inspire a head injury and so low that it rides just 21/2 inches from the ground - the lowest allowable in Europe. Once seated, the driver not only is situated as low as a supercar but also is slightly forward of the passenger, to allow both inhabitants ample shoulder room.

I, a leggy 5-foot-8, found its cockpit surprisingly spacious, if spartan. Everything about the XL1 is streamlined for maximum efficiency. Inhabitants are cocooned in a carbon-fiber monocoque that negates the need for a heavier supporting frame and is outfitted with aluminum crumple structures on the four corners, since carbon fiber is strong and lightweight but otherwise incapable of absorbing the energy of a crash.

To keep its 1,753 pounds balanced 50/50 front and rear, while simultaneously keeping the front end as low as possible for improved air flow under the car, the batteries are housed in front of the monocoque. The engine is in the back.

Drivers can select between pure EV mode, which has a range of up to 31 miles, and a hybrid mode that draws on the minuscule diesel engine of its parallel hybrid system. Both modes offered sprightly acceleration. While I didn't come anywhere close to maxing out the XL1's 99-m.p.h. top speed, it felt capable and smooth, accelerating through its seven speeds seamlessly with a dual-clutch automatic transmission and mechanical steering that added to the car's sporty driving character.

While the XL1 won't be coming to the United States, it's likely more than a few XL1 features will appear in future VW passenger cars, according to a company spokesman.