We've covered BMW's first two hybrid vehicles, just launched for the upcoming year: the 2010 BMW ActiveHybrid X6 "sports activity coupe", the world's most powerful hybrid, and the 2010 BMW ActiveHybrid 7, the world's fastest hybrid sedan.

Now a spy photo from the British magazine Autocar shows that BMW is planning to introduce its hybrid system not only for large cars, but also for its compact 1-Series.

ActiveHybrid 5 Series next?

Peter Tünnermann, project manager for the ActiveHybrid X6, had earlier told Autocar that BMW would launch its third hybrid within a year, saying "Volume models like the 3-, 5- and 7-series are clearly more suited towards a mild hybrid set-up."

2011 BMW ActiveHybrid 7

2011 BMW ActiveHybrid 7

2010 Mercedes-Benz S400 Hybrid

2010 Mercedes-Benz S400 Hybrid

Following the usual practice of pioneering pricey technology on the most expensive models, BMW will likely move down the line from the 7-Series full-size sedan to its mid-size 5-Series. So we would expect a 2011 or 2012 ActiveHybrid 5 to be launched next year.

The latest spy shot, though, shows that even the 1-Series is being tested with some sort of hybrid system. And if there's a 1-Series, then there's clearly a 3-Series hybrid being tested out there somewhere.

The test car, a 1-Series hatchback model that's not sold in the U.S.,  carries "Hybrid Test Vehicle" stickers in its side windows and on the rear bumper.

Mild hybrid system will spread

The ActiveHybrid 7 system uses some of the same hardware as the 2010 Mercedes-Benz S400 Hybrid, including the thin electric motor and the lithium-ion battery pack.

This is the system that BMW is likely to spread across the bulk of its models for global markets. Mild hybrids are relatively less expensive, require less adaptation of the core vehicle, and still provide a substantial improvement in fuel efficiency.

Joint BMW-Benz project

The two German luxury carmakers cooperated on their first mild hybrids, just as they did on adapting the Two-Mode full hybrid system to their big, U.S.-built hybrid sport utilities. BMW, like Mercedes-Benz, may be moving away from using that complex and expensive system in future vehicles.

Their approaches to mild hybrid vehicles diverged, however. BMW went for power, with better fuel efficiency as a side benefit. Mercedes-Benz chose to fit smaller engines--a smaller V-6 engine in its S400 Hybrid full-size sedan--to raise gas mileage as much as possible.