Just as we were finalizing an update of the AutoEcoRating methodology, Fisker announced the EPA certification of its plug-in hybrid supercar, the Karma. Out here in Michigan, we’ve not had a chance to test drive the Karma, but for the past few years we’d certainly been admiring the prototypes on display at auto shows. With its official data now out, we can crunch the numbers and see how the car fares on the AutoEcoRating scale.

The Fisker Karma gas-electric plug-in luxury hybrid

Propelled by dual electric motors that produce a combined 403 horsepower, the Karma can launch itself to 60 mph in 5.9 seconds. In all-electric mode, the car is rated to travel 32 miles. Once the battery’s juice gets low, a 2.0 Liter direct-injection turbocharged gasoline engine kicks in to carry the car as far as you’re ever likely to want to go with gas stations along the way. Converting combustion energy into electric current with a generator that delivers 235 horsepower, the Karma keeps its motors turning, and in this “extended range” mode of operation, fuel economy is 20 mpg.

But in all-electric mode, the Karma gets 52 mpg-equivalent. An mpg-equivalent refers to the amount of electricity that matches the amount of energy released if burning gasoline without any of the many losses that inevitably happen in an internal combustion engine.

On the AutoEcoRating scale, using our standard assumption of average U.S. electricity generation (about half from coal), the Fisker Karma scores an eRating of 118. That’s better than average, but of course, the Karma is no average car.

It’s certainly a different beast than the first plug-in hybrid on the market, the Chevy Volt, which scores 185 on the eRating scale. Our top-rated vehicle is the all-electric Tesla Roadster which, with an eRating of 267, is over twice as green as the Karma. The eRating is proportional to greenness, so that a car that’s twice as green (that is, with half the overall pollution) scores twice as high.

But these cars aren’t really the right comparisons for a luxury exotic like the Karma. A better match would be another four-door super sedan such as the Maserati Quattroporte. With a 4.2 Liter, 400 horsepower engine and a 0-60 time of 5.6 seconds, the Quattroporte’s fuel economy is 15 mpg and it rates 77 on the AutoEcoRating scale. In short, the Karma is over 50% cleaner than the Quattroporte.

Looking at carbon footprints (all based on a common assumption of 12,000 miles per year of driving), the Fisker Karma emits 5.9 tons of CO2-equivalent per year in electric mode and 7.5 tons in gasoline mode, for an average of 6.5 tons per year. The Maserati Quattroporte spews 9.6 tons per year.

So if you must and if you’ve got the budget, the Fisker Karma is the greenest in its league. Drivers who crave a unique level of passion and performance can now cruise in a much more eco-conscious way.