Used to be that potential hybrid buyers worried about whether the electric components were tough enough. Well, the growing number of Toyota Prius taxis should set that worry to rest.

Our colleagues at AllSmallCars noticed a Prius leading the Yellow Cab fleet in Denver's St. Patrick's Day parade a few days ago.

No sooner had they shown us the photo here than we ran across a story about Denver's other Prius-using taxi company, Metro Taxi--which will ultimately run no fewer than 500 Prius cabs! And because a taxi racks up 70,000 miles a year, 5 to 8 times the average, Metro says using the Prius as a taxi saves as much gas as converting 5 or more personal vehicles.

Metro Taxi says its Ford Crown Victoria cabs got about 11 miles per gallon, while it gets 50 to 60 mpg from its Prius taxis. That's higher than the EPA ratings of 48 / 45 mpg for their 2009 Toyota Prius, but we could believe it if most of their miles are stop-and-go urban traffic. That's the sweet spot for hybrids, since they can frequently switch off the engine and run on electric power. One Prius in taxi duty, Metro says, saves more than 5,000 gallons of gasoline a year.

Denver's far from the only place with Prius cabs, though. The first one appeared in Vancouver way back in 2000, and cabbie Andrew Grant drove two subsequent Priuses as well. (Toyota bought his first car, to check the condition of the battery pack, after he logged more than 200,000 miles in 25 months.)

Prius taxis have since spread far and wide, including the mean streets of New York City, though they're outnumbered in the Big Apple by Ford Escape Hybrids. Typical for New York, taxi owners are fighting a city mandate for high-mileage cabs tooth and nail.

Other US cities with Prius cabs in service include Chicago, Phoenix, Las Vegas, San Antonio, and San Francisco. Elsewhere, they can be found in Berlin, Ljubljana, Tokyo, and many other cities in Japan. And that's just a partial list.

For the record, the Toyota Prius is used as a police car as well. They can be found in Illinois, New York City, LondonCracow, Poland, Beijing, and many other locales--including Parchment, Michigan, whose Prius police cruiser caused a controversy we covered earlier.

Prius Taxi in Las Vegas by Flickr user CasketCoach

Prius Taxi in Las Vegas by Flickr user CasketCoach

[SOURCE: AllSmallCars; Prius taxi photo by Flickr user CasketCoach]