For some reason BMW's big straight 6's get better if not the same fuel efficiency than their smaller engines. From what I understand the 3.0i gets better mpg than the 2.5i and the 318i, 325i, and 328i for the E36 all got roughly the same fuel economy. Remember BMW is about power and driving experience, not an eco-tech I4 with a huge battery that kicks in as the engine shuts off in heavy traffic to conserve fuel.