TOKYO (AP) -- Toyota's Prius started out a decade ago as a risky experiment in green technology. Today, it's the world's first mass-produced gas-electric hybrid vehicle to hit the one million mark in sales.

The Prius, which went on sale in Japan in 1997, has been a big hit with drivers around the world and is now sold in 40 countries and regions. And its popularity is going strong amid surging gas prices and growing concerns about the environment.

A cumulative 1.028 million Prius vehicles have been sold globally as of the end of April, Toyota Motor Corp. said Thursday.

Toyota, Japan's top automaker, sells other hybrid models, but the Prius has been by far the most popular model. Toyota has said it plans to sell a million hybrids annually sometime in the few years after 2010.

When including the other hybrid models, Toyota's cumulative overall sales of gas-electric vehicles total 1.46 million, according to Toyota, which also makes the Camry sedan and Lexus luxury cars.

Toyota said introduction of the Prius has resulted in 4.5 million metric tons less of global warming gases compared with having standard gas engine cars on the road instead of the hybrid.

Of the more than one million Prius sales worldwide, nearly 592,000 were sold in North America and 315,000 in Japan, Toyota said.

A hybrid delivers a cleaner, more efficient ride by switching between a gas engine and an electric motor at different speeds, and by recycling the energy the car produces as it moves.

The latest Prius is estimated to deliver 48 miles a gallon (20 kilometers per liter) in city driving and 45 miles a gallon (19 kilometers per liter) on highways. Unlike standard cars, hybrids generally provide better mileage in stop-and-go city driving.