Our spy photographers have caught BMW’s new X6 hybrid being tested in California ahead of its official unveiling at the Detroit Motor Show next year.The technology was previewed at last year with a concept at the Frankfurt show, the BMW X6 ActiveHybrid concept. Developed with General Motors and Daimler, the system uses two high-performance electric motors connected to each other by three planetary gear sets. These work in conjunction with a CVT transmission delivering power from the engine – reported by insiders to probably be a version of BMW’s familiar 3.0-litre straight six petrol motor.The ActiveHybrid system also allows the car to be driven on electric power or the combustion engine alone, or with a combination of the two. A brake regeneration system similar to that already in use on some of BMW’s other models is also present, allowing the traction motors to recover energy while slowing down for storage in the onboard battery pack.Fuel consumption is expected to be reduced be 20 per cent compared to a conventional model: these savings on top of those already delivered by BMW’s Efficient Dynamics system.Despite the recent BMW X5 Vision concept previewing a diesel hybrid system, a petrol engine suits the BMW X6’s ‘sports’ appeal and will also sell better in North American, which will be the car’s biggest market. Expect UK sales to start in summer 2009.