Aug. 12--General Motors CEO Fritz Henderson Tuesday unveiled details about the Chevrolet Volt -- an electric car the company hopes will position it as a leader once again.

The sales pitch is compelling on its surface. Using a new formula specifically created for this type of electric/gasoline vehicle, GM estimates the Volt will get the equivalent of 230 miles per gallon. Lithium ion batteries, charged overnight, power the car for up to 40 miles. After that, a small gasoline-powered engine provides the power.

But the Environmental Protection Agency, which evaluates the miles-per-gallon ratings for vehicles, hasn't tested a Volt and thus couldn't confirm GM's estimates. And while representatives of the company explained that the equation they used spreads the mileage over the cost of fuel per mile driven after combining electric- and gasoline-powered miles, they didn't make that equation available for review.

Regardless, mileage half as good as what GM is touting would be a major improvement over even the most economical cars on the market. Toyota's Prius gas-electric hybrid, the most efficient car now sold in the U.S., gets 48 mpg. But with a late 2010 estimate for the Volt landing in showrooms, a rumored $40,000 price tag could stop prospective buyers in their tracks.

Henderson acknowledged that problem as a valid concern for the product's success, but worked to offset it in his overview. A $7,500 tax credit will come along with the vehicle, and he said a selling price hasn't actually been decided at this stage of development. And even though the new technology comes at a price, Henderson is confident the eye-catching fuel economy will make up for much of the related costs the consumer will be asked to bear upfront.

"Having a car that gets triple-digit fuel economy we believe can and will be a game-changer for us," Henderson said.

While the company does have a lead, GM isn't the only one in the plug-and-drive game. Chrysler Group, Ford Motor Co. and Daimler AG are all developing plug-ins and electric cars, and Toyota Motor Corp. is working on a plug-in version of its gas-electric hybrid system. Nissan Motor Co. announced last month that it would begin selling an electric vehicle in Japan and the U.S. next year. All of these vehicles will likely come at a higher cost, and whether they will sell in areas surrounding Buffalo -- the third poorest city in the nation -- remains to be seen.

The list of concerns over the cars doesn't end with the price, either. For commuters with a garage that contains a readily available power outlet, they could be a viable option.