Every year, the big car companies roll out a select few models designed for one thing: speed. Long before that happens, however, they show off a jaw-dropping show car to get everyone pumped up. Building ultra-performance machines may seem a bit insensitive given today's tightening oil supply, but there will always be a market for them, and Big Auto is starting to show us that cars can be fast and green at the same time by embracing alternate fuels. Heck, even this Sunday's Indy 500 will be paced by an ethanol-powered Corvette.

While most concept cars look like they could outrun Speed Racer's Mach 5 no problem, in reality concept cars tend to run the gamut from simple rolling bodies with no engine or drive train, to fully developed running and driving cars that you could take out on the street. The manufacturers will often throw out fanciful numbers for the performance of their dream machines, but to be quite honest, those figures are usually just the result of some educated guesswork. Even the ones that can be driven are rarely tested near the limit, so all we really know is what the computer spits out after they punch in all the numbers. That's enough for us to go on, however, and we've compiled a list of what we think are the world's fastest concept cars.

Check out the list after the break.

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At over 20 years old, the first Aerotech might seem like the geriatric grandpa of this group, but it's here for a good reason. In 1987 race-car legend AJ Foyt drove the Aerotech I to a closed course speed of 257.123 mph, a record that stands to this day. What really impresses me however, is that the engine was no more than a modified version of GM's 2 Litre Turbo Quad 4. Later versions of the Aerotech used a V-8 and broke plenty of other records, but they never quite managed to top AJ's mark.

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Once you reach a certain rarefied level, the line between concept cars and production vehicles becomes pretty blurry. While I'm sure the folks at Weber Sportscars would insist that theirs is a real production car, it's not clear how many running Faster Ones they've actually built. Still, I expect the Swiss company will be happy to take your $1.6 million check should you wish to place an order. When you get your Webber Faster One, (kind of sounds like it was named by an 11 year old), it will have a 900 bhp V-8 with GM LS7 origins, and a claimed top speed of 249 mph.

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Hennessey Performance Engineering may be a tiny company, but they have a fairly well-established track record for producing wild modified versions of already outrageous supercars. So when they hand us a drawing and say they're going to build it, we tend to believe them. The 1,000-horsepower Venom GT will use the same engine as their Dodge Viper-based Venom 1000 SRT, but this time it'll be slotted in behind the front seats in this sexy new body. Once it's built, Hennessey's computers say that the Venom GT will be able to hit 260 mph, with a 0-to-60 time of 2.4 seconds. Just the thing for a run down I-95.

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Born back in happier times before Chrysler's partnership with Mercedes-Benz fizzled, the ME Four-Twelve concept car proved what could be achieved with their combined gene pool of talent. Using an AMG-developed mid-mounted V-12 engine and four turbos (hence the name), the ME Four-Twelve was supposedly good for 248 mph and goes 0 to 60 in 2.9 seconds. There was even talk of putting the ME Four Twelve into production, with Chrysler going so far as to crash test one, but those dreams died when the wheels came off the Daimler-Chrysler bus.

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It was Acura's mid-engined NSX from 1990 which showed everyone that they were capable of producing more than just gussied-up Hondas, but that old dog finally died a couple of years back. This is what its replacement will look like, and the production version should start rolling off the lines next year. Showing a bit more of Acura's softer, more luxurious side, the ASCC seems more like a fancy GT than it's hair-shirt predecessor. But the rumored V-10 engine, up from the NSX's V-6, should provide plenty of grunt. Acura hasn't yet provided any performance figures, so it's place in the pecking order is hard to determine.

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You probably wouldn't guess by looking at it, but that zero in R Zero stands for no emissions, indicating that this stunning creation is actually an electric car. Before you go dismissing the R Zero as another tree hugger special that's all show and no go, let me tell you that the four electric motors (one per wheel) in the R Zero deliver a amazing total of 1,091 horsepower. This means that despite the weight of all its batteries, the R Zero streaks from 0 to 60 mph in less than 3 seconds on its way up to 286 mph. Now, who wants to be a tree hugger?

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While few Americans have ever heard of it, 30 years ago BMW launched a supercar called the M1 that was developed out of a stillborn collaboration with Lamborghini. The whole endeavor was a bit of a fiasco, so it's interesting that the Bavarian car maker has decided to commemorate its anniversary with the M1 Homage concept car. I know that our picture looks a bit like an artist's rendering, but that's an actual photograph of a car. Well, I should qualify that, because the M1 Homage has no mechanical bits, and is simply a design study without any plans for production. Still, it looks like it might be able to go 250 mph if they were to slot in a V-10 engine from the M5 sedan.

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Even with concept cars that are drivable, rarely do they hit more than 2 mph as they are carefully moved from transporter to display stand at the various car shows. That can't be said of the Mazda Furai, however, as it's basically an American LeMans Series race car clothed in a swanky new street legal body. The Furai's three rotor Wankel engine runs on E100 ethanol to deliver about 450 horsepower, although there's no word as to what the translates to in real on the road numbers.

Speaking of translations, Furai in English comes out as roughly The Sound of Wind, although I'm not sure if that conveys the exact nuance they were looking for.

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What's this, some kid's tweaked-out VW Golf on the list? Well, not exactly, because this is no ordinary Rabbit. Every year there's big gathering of GTI nutjobs in Austria, and VW usually trots out something special for the fans. Last year it was this über-Golf, powered by a twin turbo 6L W12 stuffed behind the front seats. With 650 horsepower on tap, this gives it a very un-Rabbit like 0 to 62 time of 3.7 seconds, along with a 202 mph top speed. Alas, this one-off car will never see production.

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Most people know that Jay Leno is a major car nut, but how many realize that he's also passionate about the environment? Of course his idea of a green-friendly supercar is somewhat removed from the norm, and after going through several design ideas on the back of a napkin, this is what he and his team came up with. The EcoJet is based around Corvette C6 chassis components housed under a sleek Cadillac-inspired body, but instead of a big V-8, there's a Honeywell LT-101 jet engine that runs on biodiesel mounted behind the seats. That's good for about 650 horsepower, although other performance figures were not released.

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One mistake that manufacturers sometimes make is to take deposits from customers for a new model based on the concept version. This is what happened to Jaguar after it started showing off the XJ220 concept at car shows in 1988. They took literally hundreds of orders with cash deposits for the V12 four-wheel drive supercar, only to discover that they couldn't actually make a street-legal version with all of those features intact. By the time they finally delivered the first customer car, the big V-12 had shrunk to a 3.5L V-6, and the four-wheel drive was gone. Customers were pissed, and some demanded their money back. Ironically, the production version's performance was actually very similar to the prototype, which was capable of 0 to 60 mph on 3.5 seconds and over 200 mph.

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Okay, so it's technically not a car, but the Tomahawk does have four tires, so we're including it. The Dodge Tomahawk shows just what happens when you take a 500-horsepower Viper engine, and build something kind of like a motorcycle around it. Tipping the scales at less than half the weight of most supercars, the published performance figures of 0 to 60 mph in 0.75 seconds with a top speed of 750 mph are guaranteed to generate a double take. Of course these figures are just theoretical (another Dodge release pegged the top speed at 420 mph), as nobody has yet had the cojones to test the Tomahawk's true potential. Amazingly, Dodge built 10 copies of the Tomahawk which were then sold through Neiman Marcus for a cool $550,000 each, as a non-running "rolling sculpture."