General Motors today detailed the highly anticipated fuel economy label for the Chevy Volt, and it varies greatly depending on driving habits.

The EPA fuel economy label on the gas-electric Chevy Volt gives it a combined rating of 60 miles per gallon. There are separate ratings for electric-only driving, which is 93 "miles per gallon equivalent," and for gas-only driving, which is 37 miles per gallon.

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On a full battery charge, the Chevy Volt, which GM hopes to start selling next month, drives about 35 miles. After that distance, a gas engine kicks in to run a generator that charges the battery.

In a call with reporters, GM executives took pains to point out that mileage will vary greatly depending on how frequently drivers recharge. "If you try to boil it down to a single number, it becomes quite difficult," said Tony DiSalle, Chevrolet product marketing director.

The Volt label provides additional information geared at showing the variety in miles per gallon and cost per mile a driver can expect. It shows that the cost per mile ranges from 4 cents per mile for 30 miles up to 9 cents per mile on gas only. Miles per gallon of gasoline can be as high as 168 mpg for a distance of 45 miles.

With the rating, the Volt qualifies as the best car in the compact-car category on fuel economy, and it rates relatively well on greenhouse gas emissions and air pollutants.

Nissan on Monday announced that the all-electric Nissan Leaf will have a fuel economy rating of 99 mpg-equivalent. The Volt fuel economy in electric-only mode is 36 kilowatt hours per 100 miles, compared with 34 kilowatt hours per 100 miles for the Leaf.

Last year, GM announced that it expected to get 230 miles per gallon on city driving. Today, GM executives said that rating was based on an earlier methodology from the Environmental Protection Agency.

GM says that the electric range of the Volt will be between 25 miles and 50 miles depending on driving patterns, terrain, and weather conditions.

The Volt label is unique in that it provides more information than a typical fuel economy label. GM expects that potential buyers for the $41,000, four-person sedan will be willing to spend some time understanding how mileage can vary, said Doug Parks, Chevrolet Volt's global vehicle line executive.