A new survey finds that more than 90 percent of respondents are concerned about the environment, according Kelley Book, with 31 percent purchasing a more fuel-efficient car.

In most cases, cars that are fuel efficient are also environmentally friendly. Using Environmental Protection Agency data, Forbes has ranked the cleanest driving cars on the road.

Not surprisingly, hybrids figure prominently on the list.

"Environmental consciousness tends to come from wealthier, college educated people," Mike Omotoso, senior manager of global powertrain forecasting for J.D. Power and Associates told Forbes. "But as terms like 'global warming,' 'dependence on foreign oil,' and 'carbon footprint' become more common, more and more consumers at all income levels will factor in the environment in their vehicle purchase decision."

J.D. Power expects more than 1 million hybrid vehicles to be sold in the U.S. by 2012. By then, Omotoso told Forbes there will be more than 80 hybrid models to choose from.

The Toyota Prius tops the list of most environmentally friendly cars to drive, with an EPA air pollution score of 9.5 on a scale of 1-10 and a carbon footprint -- the annual tons of greenhouse-gas emissions -- of 4.

A few hybrid SUVs, like the Ford Escape Hybrid, which tied for fourth place, and Toyota Highlander Hybrid, in fifth, also placed well.

The highest-rated gas-powered vehicle is the Ford Escape, which ranked sixth.

Many of the lowest-emission versions of some models aren't available in all 50 states. Some certified "super low-emissions" or "partial-zero emissions" vehicles are offered only in California and the handful of other states that adhere to California's stricter air-pollution standards. They include Arizona, Connecticut, Florida, Maine, Maryland, Massachusetts, New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Vermont, and Washington.

Least Polluting Cars
RANK	CAR	AIR POLLUTION SCORE	CARBON FOOTPRINT
1	Toyota Prius	9.5	4.0
2	Honda Civic Hybrid	9.5	4.4
3 (tie)	Toyota Camry Hybrid, Honda Civic GX*	9.5	5.4
4	Ford Escape/Mercury Marnier Hybrids	9.5	5.7
5	Toyota Highlander Hybrid	9	7.1
6	Ford Focus	8	6.6
7	Smart Fortwo	7	5.1
8 (tie)	Mini Cooper/Clubman, Toyota Yaris	7	5.7
9	Toyota Corolla	7	5.9
10	Kia Rio	7	6.3
Source: Forbes.com, Environmental Protection Agency *The Honda Civic GX is a natural gas-powered vehicle currently sold only in New York and California.