General Motors Corp.’s upcoming Chevrolet Volt rechargeable electric car would have the best mileage among all mass-produced hybrid vehicles and would surpass Toyota Prius’ fuel economy by more than four times.

General Motors Corp. CEO Fritz Henderson announced the news to the press on Tuesday.

The Chevrolet Volt extended-range electric car was given an official Environmental Protection Agency (EPA) rating of more than 230 miles per gallon of gasoline in city driving and a combined city-highway average fuel economy of more than 100 miles per gallon.

The Volt is powered by an electric motor and a battery pack that could be recharged from a standard home electrical outlet. The battery pack has a 40-mile range. After that a small internal combustion engine kicks in to generate electricity for a total range of 300 miles.

“From the data we’ve seen, many Chevy Volt drivers may be able to be in pure electric mode on a daily basis without having to use any gas,” said Henderson. “EPA labels are a yardstick for customers to compare the fuel efficiency of vehicles. So, a vehicle like the Volt that achieves a composite triple-digit fuel economy is a game-changer.”

The Volt is at the forefront of General Motors’s effort to reinvigorate its business, after losing market share in the U.S. to Ford Motor Co. and its Japanese rivals. The federal government awarded the automaker with the largest share of $2.4 billion in federal grants for the development of battery powered vehicles--committing nearly $400 million to help the company build the much anticipated Chevy Volt plug-in hybrid prototype.

GM already received about $50 billion in federal help to restructure and make it through its recent bankruptcy. The help from the federal government includes approximately $150 million for the Volt program and $100 million in investments for production of future electric vehicles.

Domestic competitors Ford Motor Co. and Chrysler Group were awarded $30 million and $70 million apiece. With a line-up of 25 new GM vehicles due to be launched by 2011, Volt is expected to dwarf any mass-market brands including Toyota’s Prius. One of the company’s restructuring efforts is to create a “green” image among consumers, in which the Volt is a key element.

But the EPA said in a statement released Tuesday that the agency has not tested a Volt “and therefore cannot confirm the fuel economy values claimed by GM.” EPA said it applauded “GM’s commitment to designing and building the car of the future—an American made car that will save families money, significantly reduce our dependence on foreign oil, and create good-paying American jobs.”

GM estimates that the Volt’s price tag will be about $40,000, though the automaker says that the price is expected to drop with future generations of the Volt and up to $7,500 in government tax credits.

Currently, GM is manufacturing 10 Volt vehicles per week, and so far has made 30 cars, according to the company’s technical center in Detroit.

“The 230 city mpg number is a great indication of the capabilities of the Volt’s electric propulsion system and its ability to displace gasoline,” said Frank Weber, global vehicle line executive for the Volt.

“Actual testing with production vehicles will occur next year closer to vehicle launch. However, we are very encouraged by this development, and we also think that it is important to continue to share our findings in real time, as we have with other aspects of the Volt’s development.”

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