Fisker Automotive made news today by setting a somewhat realistic mileage figure for a plug-in car.

The company, which will show off its Fisker Karma next week at the Frankfurt Auto Show, said that the plug-in Karma will consume about 3.5 liters for every 100 kilometers of driving, according to calculations developed by the Society of Automotive Engineers.

There are 3.785 liters per gallon, giving the Karma a rating of 100 kilometers per 0.925 gallons of gas, or 108.1 kilometers per gallon. In miles, that comes to around 67.6 miles per gallon. (It is unclear at the moment whether or not the figure includes the electricity required to charge the battery: We are checking.) The average car in the U.S. gets about 22.4 miles per gallon. The Karma is a serial hybrid: It drives on electricity for the first 50 miles, but a gas engine recharges the battery while the car drives.

As a result, the Karma will cost 3 cents a mile to drive versus 7 cents for a regular gas car. The Karma, though, will also cost $87,900 and a good portion of that price revolves around the battery. It contains a 22 kilowatt/hour battery and many battery experts estimate that lithium-ion batteries for cars cost around $900 to $1,000 per kilowatt. The goal is to get it down to $300 to $500 in the next several years.

The Karma goes on sale in 2010, a delay that will see it released during the same year as a host of other plug-in and all-electric cars.

The mileage rating gives the four-door luxury Karma a mileage rating similar to some of the plug-in hybrids currently being tested today. Google has achieved a mileage of 93.5 miles per gallon on a Prius outfitted with extra batteries, but that car was driven by a professional driver on a circumscribed course in fair weather. In ordinary conditions, some of the cars owned by Google have achieved a 66 mile per gallon rating. The Department of Energy in extensive tests got 51 miles per gallon on retrofitted plug-in hybrids.

The figure will likely stoke the debate over the efficiency of electric and plug-in cars. Both General Motors and Nissan have issues triple figure mileage ratings for, respectively, the Volt and the Leaf. General Motors has said that the Volt will get 230 miles per gallon while Nissan has said the all electric Leaf will get 367 miles per gallon. Those figures in part depend on calculations that assume that most drivers will only go about 40 miles a day.

Tesla Motors, by contrast, has said that its all-electric Roadster gets about the equivalent of 135 miles per gallon.

Image of the Karma via Fisker.