The Chevrolet Volt, which runs on electricity that comes from batteries and gasoline, will get an estimated city fuel economy of 230 miles per gallon and is expected to go on sale in late 2010, General Motors Co. announced today.

The Volt is expected to travel up to 40 miles on electricity from a single lithium-ion battery charge before switching over to gasoline to extend its range to more than 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 GM Chief Executive Officer Fritz Henderson, who pointed to U.S. Department of Transportation data indicating that nearly eight of 10 Americans commute fewer than 40 miles a day.

According to GM, a Volt would consume as little as 25 kilowatt hours per 100 miles of city driving, so with the average cost of electricity at 11 cents per kWh, a driver would pay $2.75 to travel 100 miles (2.75 cents per mile). One hundred miles of city driving in a car getting near 30 mpg with gas at the AAA national average of $2.64 per gallon would cost a driver $8.80 (8.8 cents per mile).

The car could get as much as 50 mpg in gasoline mode; the Toyota Prius gets 46 mpg. The difference is that while the Prius gets all of its energy from gasoline, the Volt achieves its 230 mpg figure because it will have already gone 40 miles on battery power without using any gas.

A CNNMoney calculation breaks it down: If the car is driven 50 miles, during the first 40 miles no gas is used and during the last 10 miles 0.2 gallon is used. In other words, you would drive 50 miles on 0.2 gallon of gas, or 250 miles per gallon. If the driver goes 80 miles without a charge, however, the gas economy drops to 100 mpg, then 62.5 mpg if it goes 300 miles.