More vehicles than ever before require owners to fill the tank with premium-grade gasoline, but fewer drivers are bothering to do so, an anomaly experts say is driven by near-record prices at the pump.

In 2007, the Energy Information Administration says, premium gas claimed 9.4 percent of retail gas. That’s a far drop from a couple of decades ago, when premium claimed as much as 40 percent of the market, according to Tom Kloza, chief oil analyst at the Oil Price Information Service. Some dealers in well-heeled suburbs regularly moved 50 percent premium, Kloza said.

Since then, there has been a steady decline in premium sales.

The trend has occurred even though car manufacturers are turning out more vehicles designed to run on premium. The number of new vehicle models that should run on high-octane fuel has increased to 279 in 2008 from 167 in 2002, according to Robyn Echard, a spokeswoman for Kelley Blue Book, an auto pricing guide.

“Most cars today require premium, and most of these are higher-performance or sport vehicles,” Echard said.

That has not stopped motorists from settling for regular during a summer when gas prices topped $4 a gallon – and high-octane premium gasoline often sold for 20 cents to 40 cents more than regular.

“With prices high, it’s tough to get those premium customers back, unless you operate in an area that has lots of limousines or vehicles for real car aficionados,” Kloza said. He estimates regular octane now accounts for somewhere between 75 percent and 80 percent of the market.

Drivers who fail to put premium in their car despite the manufacturer’s recommendation do run a risk, according to Wade Newton, a spokesman for the Alliance of Automobile Manufacturers.

“If your car requires premium and you do not use it, it is a violation of your warranty,” Newton said. “It affects performance and can clog your system. It does have the potential to cause adverse effects.”

But some mechanics and manufacturers argue premium could end up saving motorists money in the long run, despite high gas prices, because higher-octane fuel makes the car engine perform more efficiently, resulting in better mileage per gallon.

It’s an argument that has convinced Mary Falcone, a Westfield, N.J., resident who commutes about 50 miles each day in her new Toyota Corolla. The manufacturer estimates the car will get 35 miles per gallon, but Falcone says she usually gets 40 mpg after filling up with premium.

“If I’m getting 5 more mpg, it’s worth it to me,” said Falcone, who spent $4.19 per gallon filling up her car at a Gulf station last week.

The price was 35 cents more than regular.

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