Consumers considering a hybrid vehicle are now a majority, according to a survey released today by JD Power and Associates. The number jumped to 62 percent this year, from an even 50 percent in the same survey last year. The reason? For 7 out of 10 respondents, it was “lower fuel costs” or “better fuel economy.” And what about “being better for the environment?” Just 16 percent said that was why they’d pick a hybrid.

The gradual but steady rise over the past several years likely reflects growing knowledge about what hybrids can and can’t do for mileage, along with revised calculations to reflect the recent run-up in retail gas prices.

Fully eight of the top 30 models in the Automotive Environmental Index were hybrids: four from Toyota and Lexus, two from Ford and Mercury, and one each from Honda and Nissan. That index combines EPA data on fuel economy, exhaust emissions, and greenhouse gases with customer feedback on initial vehicle quality and how real-world mileage varies from stated fuel economy.

The survey shows that the mileage reported by hybrid owners is now far more consistent with government figures. Earlier surveys of Prius owners showed them getting as low as 81 percent of the mileage shown on the new-car sticker, said Mike Marshall, Power’s director of automotive emerging technologies. “Hybrids are still below the EPA figures,” he told, “but they’re not at four fifths any longer.” The changes to the ratings for 2008 models reflect a downward revision by the Environmental Protection Agency, to reflect real usage patterns better.

In contrast to hybrids, consideration of flex-fuel and clean diesel vehicles fell. Flex-fuel dropped from 47 percent in 2007 to 43 percent, and clean diesel plummeted by almost a third, from 23 percent last year to just 16 percent this year. The survey was conducted in May and the first week of June, by which time diesel prices had soared far above their traditional parity with gasoline.

More than 4,000 consumers planning to buy a new vehicle within two years took part in the survey, formally known as the JD Power 2008 Alternative Powertrain Study. It’s the third such annual look at why consumers consider or reject vehicles with power sources other than strictly gasoline. The study dates back to 2005, when Marshall noticed in a different survey that consumer interest levels in hybrids and clean diesels was high enough to spawn a more detailed survey.

This year’s version of that earlier survey offered just a quick snapshot of consumers’ interest in hybrid powertrains. There, 72 percent of respondents said they were “definitely” or “probably” interested in a hybrid for their next vehicle, before they learned the price premium. Once they knew that figure—Power used a $5,000 premium—the “definitely/probably” group fell to 46 percent of the respondents. Of the 20 technologies, hybrids ranked fifth most popular before pricing, and eighth afterward.

The earlier study focused on the tradeoffs consumers make in selecting among new choices in communications, safety, and information technology features, said Marshall. He had put questions on both hybrids and clean-diesel technologies back into that survey, he told, to “see what they’d trade off when they had a limited amount to spend”—not to understand how consumers viewed hybrids in any detail.