Prius sales need a charge

A decade after the Toyota Prius became a hit as the first hybrid to attract large numbers of buyers, sales of the popular car need a charge. Through May of this year, Prius sales in the United States are down 7.8 percent while sales for all vehicles have risen 7.3 percent.

Has the car that has become synonymous with hybrids lost its mojo?

"People no longer feel like they have to get a Prius in order to buy a hybrid," said Jessica Caldwell with Edmunds.com. "It's time for the Prius to move on and for Toyota to find new ways to market it."

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Low Gas Prices & Increased Competition Cutting Into Sales

It would be a stretch to say Prius, the most popular car in California, is running out of gas. After all, Toyota still expects to sell almost a quarter of a million Prius models in the U.S. this year. That will likely make Prius one of the top 20 best-selling vehicles in the U.S. in 2013. So this is not a dog car.

However, the Prius is no longer the red-hot model it was back in 2007 and 2008, when it generated so much buzz dealers had waiting lists that stretched out for months as buyers paid well over sticker price for the hybrid.

What Has changed?

Gas prices and competition. Right now, there are 38 different hybrid models being sold in the U.S., including four versions of the Prius. For car buyers, there are simply more options when it comes to hybrids.

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"Toyota needs to work harder to differentiate the Prius from the competition," said Caldwell.

Meanwhile, moderate gas prices mean there's less of a clamor in the market for hybrid vehicles. Yes, hybrid sales are still growing faster than industry sales, but with gas under $3 a gallon there's no frenzy for ultra fuel efficient cars.

New Marketing, New Prius Push

Toyota executives are well aware the Prius may be entering a more mature part of its growth cycle. It is now like any other model, a vehicle that will require marketing support and ad campaigns to keep sales moving. In fact, this month Toyota will roll out a new ad campaign specifically centered around the Prius.

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"We've been focused on other, new models we've launched this year," said Bill Fay, Toyota Division General Manager. "May was a really good month for Prius and our plan is to keep that momentum through the summer."

Fay noted he's confident Prius sales can grow in the second half of the year and Toyota's hybrid could post positive sales by the end of the year.

Still Quirky Enough to Make a Statement

There's one other factor that could be playing a role in the slowdown of Prius sales. Is this car still quirky enough to be cool? When the Prius first came out, its unique look was one reason many people bought the car. It was a way to make a statement. Those days are gone.

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"Part of the Prius' appeal when it came out was the fact it was so unique looking. Now, it has become so popular its uniqueness is gone," said Caldwell. In fact, more than 1.4 million Prius models have been sold around the world and in some places you don't have to look far to find one.

California is a good example. Last year, Toyota sold more than 60,000 Prius models in the golden state. It was the top-selling car in the state and nearly one out every five subcompacts sold in California was a Prius.

That kind of popularity is a double-edged sword for automakers. The Prius is still one of the most popular cars on the road, but these days it will take a little more work for Toyota to keep Prius sales rolling.

—By CNBC's Phil LeBeau. Follow him on Twitter @LeBeauCarNews

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