How a car that runs on steam doubled in value over the past 5 years

On this week's episode of CNBC's "Jay Leno's Garage," auto appraiser Donald Osborne uses his encyclopedic knowledge of cars to teach the host a thing or two about alternative fuel sources.

Osborne assesses and caresses three vehicles, none of which run on regular gasoline.

Which one do you think has recently appreciated the most?

1979 Mercedes-Benz 300D

At an MSRP of $20,911, this Mercedez doesn't look unusual, but looks can be deceiving. The '70s classic runs on bio-diesel.

As Osborne notes, compared to your typical gas guzzler, that means the engine has fewer parts and a lower operating cost.

"You drive to your favorite Chinese restaurant. When you finish dinner, you ask them for the check and also for the oil that they fried your pork fried rice in, and then just put it in the car and you drive home," jokes Osborne.

In actuality, it's "not quite that simple at all," says Leno. Bio-diesel is based in vegetable oil or animal fat, but it's often blended.

1989 Morgan Plus 8

This traditional English sports car, which originally sold for $35,000 at a time when manufacturers were racing to meet emission standards, runs on propane.

"Propane burns more efficiently than gasoline does, so it actually provides a higher octane and better combustion, which gives you more performance," Osborne tells Leno. "The problem is: The infrastructure for getting propane is not that for getting gasoline," because, though propane is more efficient, gas is cheaper.

1953 Paxton Phoenix

Oldest and perhaps most intriguing of the three, this high-end fiberglass luxury car is a personal favorite of Osborne. It's powered by steam.

To produce the car, 20th century entrepreneur Robert Paxton McCulloch consulted with Abner Doble, an engineer who designed over 40 unique car prototypes and who is a personal hero of Leno's.

"He produced the greatest steam car ever made: The only steam car where you turn a key and drive away," says Leno. "I have two of them."

The Phoenix never made it to production, notes Osborne, because of hold ups at the steam power plant. Had it gotten to the market, it would have cost around $10,000 in the early 1950s, a time when the average car cost between $2,000 and $3,000.

This one appreciated over 100 percent in the past five years from a value of $175,000 to $375,000. According to Osborne, that's because of a recent rise in public interest interest in one-offs, prototypes and concept cars.

What about the others? Have they appreciated more or less? Watch the video to find out.

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CNBC's "Jay Leno's Garage" airs Thursdays at 10 p.m. EDT.

Video by Richard Washington