There’s no question that people love the idea of compressed-air cars, which have long been under development by the French company Motor Development International and, according to a company spokesman, could be on American roads (after many delays) by 2012.

“It sounds ideal, like we could be free from the constraints of petroleum dependence,” said Andrew Papson, a transportation engineer and associate at the consulting firm ICF International.

But as much as the idea is attractive, Mr. Papson is skeptical about air cars. He finished graduate studies at the University of California, Berkeley, last year and was part of a team at the school that published a paper this week that was critical of air-car claims.

The “Economic and Environmental Evaluation of Compressed-Air Cars,” published in Environmental Research Letters, examined the life cycle of the compressed-air car and concluded that the air car “fared worse than the battery-electric vehicle in primary energy required, greenhouse gas emissions and life-cycle costs, even under very optimistic assumptions about performance. Compressed-air-energy storage is a relatively inefficient technology at the scale of individual cars and would add additional greenhouse gas emissions with the current electricity mix.”

Mr. Papson, who has co-authored a second academic paper that will be presented at the 2010 Transportation Research Board annual meeting, said that compressed air holds less than 1 percent of the energy of gasoline. In an e-mail message, he said that his calculations (based on specifications he said he obtained from M.D.I.) show that the air car would likely have a range of 29 miles. According to the research board report, air cars are “ultimately not viable, comparing poorly to gasoline and electric vehicles in all environmental and economic metrics.”

“Compressed-air cars sound very nice, and they share with electric cars the advantage of not producing any local air pollution on the road, as well as being able to charge from the grid, but electric cars are much more efficient,” said Felix Creutzig, a co-author and post-doctoral fellow, in an e-mail message. “Electric cars are about three times more efficient than compressed-air cars.”

The Environmental Research Letters report does conclude that a hybrid car combining compressed air with a gas engine “is technologically feasible, inexpensive and could eventually compete with hybrid electric vehicles.”

Zero Pollution Motors of New Paltz, N.Y., is licensed to produce compressed-air cars in the United States, said the company’s chief executive, Shiva Vencat, and could do so by 2012. According to Mr. Vencat, the company will start production in Nice, France, in the first quarter of 2010. He said air cars (there are several models that have been shown) have a range of 120 miles at what he called “urban speed.” A proposed range extender, which heats the air with a variety of fuels, including propane or vegetable oil, will be on the second generation of cars.

Asked about academic challenges to the compressed-air car, Mr. Vencat said, “Buy a ticket, go to Nice and try one.”