The Chevrolet Volt will be rated as averaging at least 230 miles per gallon in city driving conditions, GM has announced.
Speaking at a news conference, GM chief executive officer Fritz Henderson explained that the US authorities have reached a draft legislation for how to rate the fuel economy of plug-in electric vehicles.
Details of how the calculations will be made have not been made public, although it has been announced that it is dependent on how long the battery-only mode lasts and how often the engine is running during the test process.
According to these figures, the Volt will be rated at 230mpg in town and more than 100mpg on average when it goes on sale in November 2010. These figures are rated in US miles per gallon, not imperial.
The US Environmental Protection Agency, which rates fuel consumption on all cars, currently says the Toyota Prius is the most fuel-efficient vehicle on the market.
It is rated at 51mpg in city driving and 48mpg on the motorway, although these figures are not calculated using the same method as the Volt.