Yes, the 2014 BMW 7-Series lineup is big, spacious, luxurious, and powerful; but that doesn't entirely preclude fuel efficiency. Depending on which model in the lineup you choose, the 7-Series can, simultaneously, be surprisingly good on gas.
Gas mileage ranges up to 28 mpg highway for 6-cylinder models, up to 30 mpg with the ActiveHybrid 7. On V-8 cars, it's as good as 25 mpg highway with rear-wheel drive.
The same 16/24 mpg rating is applied to both the short- and long-wheelbase twin-turbo Alpina B7, the high-performance edition of the 7-Series, while the V-12 760Li gets just 13/20 mpg.
Throughout the lineup, the 7-Series gets a suite of fuel-saving technologies: auto start-stop, brake energy regeneration, and an ECO PRO mode. Auto start-stop turns off the engine at idle, for instance at a stop light, and restarts it when the driver lets off the brake. And Brake energy regeneration captures some of the energy that would otherwise be lost in braking.
The driver needs to select ECO PRO mode, but it functions mostly unobtrusively, managing powertrain behavior and programming of the heating, air conditioning, heated seats, and exterior mirror heating to maximize efficiency. With it you also get a coasting mode that can decouple the engine from the transmission, allowing extended coasting at speeds of up to 100 mph. And in some conditions in the ActiveHybrid 7, the engine completely shuts off during coasting mode, restarting only when you reaccelerate.