DaimlerChrysler AG and BMW AG have announced a partnership to develop a hybrid drive system for luxury cars, The Associated Press reports. The two companies said they would work on a so-called "mild" hybrid system for rear-wheel-drive vehicles. That type of system is more efficient than a standard motor because it draws power from two energy sources, typically a gas or diesel engine combined with an electric motor, but less so than a full hybrid. The system would be developed in Germany and should be available in vehicles within three years, the companies said in a joint statement. Working together would allow them to pool development, testing and quality control resources, they said. The agreement would expand the cooperation between the two companies already started in 2005 at a hybrid development center in the United States, according to The Associated Press. Though they would be working together, the companies say their final products would remain distinct because the technologies will be tailored to fit the different vehicles.