15 years ago the Prius was an oddity, an ice-breaker at cocktail parties... and today it's the world's third best-selling car line, driven by U.S. demand and incentives in Japan, according to Bloomberg.

Prius sales have more than doubled and rebates and tax breaks are saving buyers in the ballpark of $2,500 or more. In the last quarter sales soared to more than 247,000 vehicles trailing only Toyota's Corolla (301,000) and Ford's Focus (277,000) sales. And the hybrid line also gives the Toyota brand three of the top 10 models in the U.S. so far this year.

Clearly, the hybrids are here to stay. "It proves Prius wasn't a fluke, there's a long-term market for hybrids," says Eric Noble, president of the Car Lab, an automotive consultancy in Orange, CA.

In the aftermath of last year's earthquake and tsunami that cut auto production and parts production, the government began encouraging purchases of fuel-efficient vehicles to reverse sagging domestic sales.

Sales for the vehicle in Japan have been driven by rebates equal to 100,000 yen (approximately $1,258) and tax savings there also reduce the price by another $1,258. The average price for a Prius in Japan is about $25,000.

Analysts say Toyota is introducing good vehicles like the Aqua and assuming that it will maintain healthy sales volume in Japan even after the subsidies end. Undoubtedly they believe the vehicles will have the same staying power in the U.S. too.

Prior to the natural disasters that struck Japan, Toyota ranked as the world's largest automaker by sales from 20008 to 2010. Sales of Toyota, Lexus, Scion, Hino and Daihatsu grew to 2.4 million in the quarter, ahead of GM's 2.2 million and Volkswagen's 2.1 million according to Bloomberg data.

Since the start of Prius sales in 1997, Toyota has sold 4 million hybrid electric vehicles worldwide, including 1.5 million in the U.S.

John Wolkonowicz, an independent analyst in Boston and expert on automotive history adds that the sales pace for Prius isn't likely to be matched any time soon by any other hybrid models. Why? Because Prius was the first hybrid on the block. "Prius' popularity gives it marketing benefits. "It provides a 'why buy?' reason for customers who may be on the fence," he noted.

But, Wolkonowicz says, "We should see hybrid sales drop again as gas prices fall and we won't truly see hybrids take off in the U.S. until we get to $5 gas and it stays."

Here's hoping we never get there.