The surging cost of gasoline and a desire for a greener commute are turning more people to electric bikes as an unconventional form of transportation.

They function like a typical two-wheeler but with a battery-powered assist. Bike dealers, riders and experts say they are flying off the racks.

A group that does market research for the National Bicycle Dealers Association estimates 10,000 electric bikes were sold in the U.S. in 2007. That's up from 6,000 in 2006. They're even more popular in Europe, with about 89,000 sold in the Netherlands and 60,000 in Germany last year.