Leonardo DiCaprio and Paris Hilton can have their hybrid vehicles, but if they truly want to prove how green they can be, they'd be better off buying an older, used vehicle. In fact the new issue of Wired points out manufacturing a new Toyota Prius - Leo's choice of wheels - requires 113 million BTUs. There are 113,000 BTUs  in a gallon of gasoline. You do the math.

Okay fine, if you're mathematically-challenged, that works out to the equivalent of 1,000 gallons of gasoline before the Prius even makes it onto a dealer's lot. The owner of a new Prius won't break even on their carbon debt until they've driven roughly 46,000 miles.

Then consider an older car that has already been manufactured some time ago and is looking for a good home. Not all cars are made equal, so make sure you look for fuel-efficient models such as the 1998 Toyota Tercel or the 1994 Geo Metro XFI. The Tercel gets 27 miles per gallon in the city and 35 miles per gallon on the highway; in comparison, the Prius would have to travel 100,000 miles to reach the same carbon savings. The Geo Metro and the Prius are equal at 46 miles per gallon, so the Prius would never even be able to catch up in terms of carbon saving to that particular option.

Other options to consider: the Mazda Protege (mid 1990s), the Dodge Colt (early 90s) a 1985 Chevrolet Chevette or a 1987 Chevrolet Sprint. If you'd prefer to find a fuel-efficient vehicle made in the past 10 years, try the Toyota Echo, the Honda Civic, a Chevrolet Prizm or a Mini Cooper.

As an added incentive, you'll probably find one the the aforementioned options - or most older cars for that matter - come with a more appealing price tag than a brand-new hybrid will. Going green and saving some too; let's see Leo and Paris boast that!

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