WASHINGTON — The Nissan Leaf, an electric car aimed at attracting environmentally conscious motorists, will get the equivalent of 99 miles per gallon in combined city and highway driving, based on government testing.

Nissan said the Environmental Protection Agency’s fuel efficiency window sticker, which provides information about the car’s energy use, would estimate the electric car will achieve the equivalent of 106 mpg in city driving and 92 mpg on the highway.

EPA’s tests estimate the Leaf can travel 73 miles on a fully charged battery and will cost $561 a year in electricity. Nissan has said the Leaf can travel 100 miles on a full charge, based on tests used by California regulators. Nissan and General Motors are both releasing electric cars within weeks in the industry’s most prominent attempt at mass-producing vehicles that shift away from petroleum. The Leaf does not have a gas engine and must be recharged once its battery is depleted.

The tests show equivalent fuel efficiency of nearly twice the Toyota Prius, which gets 50 mpg in combined driving.

GM’s entry, the Chevrolet Volt, uses an electric battery for the first 25 to 50 miles and a small gasoline engine to generate electricity once the battery runs down. The gasoline engine can generate power to run the car another 300 miles. GM has not yet revealed the mileage rating for the Volt.

Mark Perry, Nissan North America’s director of product planning, said the vehicle’s range would vary based on driving conditions. Tests conducted by the Federal Trade Commission, which regulates advertising claims, had estimated a range of 96 to 110 miles per full charge and the company’s internal tests had found a broader range of 64 to 138 miles.