For 2010, BMW is releasing two hybrid vehicles that are very different both in style and in their approach to using electric power to assist the gasoline engine.

We've already covered the 2010 BMW ActiveHybrid X6 "sports activity coupe", which uses the Two-Mode Hybrid system jointly developed by General Motors, Daimler, Chrysler, and BMW.

BMW's mild hybrid full-size luxury sedan

Now reviews of the second car, the 2010 BMW ActiveHybrid 7 sedan, are starting to filter out. It's one of a growing number of luxury hybrids from BMW, Cadillac, and Mercedes-Benz that join Lexus (who created the category), with Fisker arriving next year as well.

It's a mild hybrid, meaning that its electric motor restarts the engine after it shuts off at stops and also adds torque to assist the gasoline engine. But unlike such full hybrids as the ActiveHybrid X6, it cannot travel on electric power alone.

World's "fastest hybrid sedan"

Car and Driver was among the first to test the hybrid 7-Series, saying it "seems to actually make sense" [sic] relative to some other vehicles in "Bavaria's barrage of the bizarre," including the BMW X6 and the BMW 5-Series Gran Turismo.

Similar to the title of "most powerful hybrid in the world" for its ActiveHybrid X6, BMW dubs the hybrid 7 to be "the fastest hybrid sedan in the world."

Autobahn "rocket"

It's faster than the BMW 750i, which uses a similar V-8 engine, though the hybrid 7 is both slower and less expensive than the low-volume V-12 BMW 760Li.

A "brief blast up the autobahn," Car and Driver says, "confirms that the hybrid 7 rockets to its 150-mph governor without any of the lethargy commonly associated with hybrids." And the magazine saw an indicated 20 miles per gallon in usage more like that of typical U.S. drivers.

Typical buff-book sneer

The regenerative brakes were well-integrated, according to the long-established buff book, though the test driver found that the hybrid 7 jerked if he accelerated just as the engine was shutting off at a stop. The engine shut-off can be disabled by putting the transmission into Sport mode, however.

In the end, given its typical sneers toward anything with electric drive other than a Tesla Roadster, it's probably not a shock that Car and Driver dismisses the 2010 BMW ActiveHybrid 7 as "goofy".

Another joint BMW-Benz project

The ActiveHybrid 7 uses some of the same hardware as the 2010 Mercedes-Benz S400 Hybrid, including the lithium-ion battery pack and electric motor. As they did (with other partners) on the Two-Mode Hybrid project, the German luxury carmakers cooperated on their first mild hybrids.

But unlike BMW, Mercedes-Benz fitted a smaller V-6 engine to its hybrid full-size sedan to maximize fuel efficiency, giving gas mileage of 25 miles per gallon or better in real-world usage.

More mild models?

BMW is likely to extend its homegrown mild-hybrid system into other models. Peter Tünnermann, project manager for the 2010 BMW ActiveHybrid X6, told the British magazine Autocar that the company would launch a third hybrid within 12 months.

Which model? He didn't specify precisely, but he did say, "Volume models like the 3-, 5- and 7-series are clearly more suited towards a mild hybrid set-up on the basis of their packaging and broad appeal." We expect the 5-Series to be BMW's next hybrid.

No pricing yet

The 2010 BMW ActiveHybrid 7 will go on sale early next year; the company hasn't yet released prices for this model, though it will cost more than the BMW 750i, which starts around $80,000.

We look forward to our first drive in BMW's second hybrid, and will bring you driving impressions as soon as that happens.

Check out every day (or sign up for our free e-mail) to see more road tests of new hybrids and other green cars for the 2010 model year.

[Car and Driver, Moneywatch, Autocar]