Audi S6 vs BMW 8 Series: Specs Compared

Running cost over five years: at the EPA's 15,000-mile-a-year assumption the BMW 8 Series burns about $3,050 of fuel annually against $3,450 for the Audi S6. That $400 yearly gap compounds to roughly $2,000 over five years and $3,200 over eight — often more than the price difference between two trims of the same vehicle, and the single largest running-cost line item separating these two.

City and highway economy: the BMW 8 Series leads in both cycles — 23 mpg city and 30 mpg highway against 19 and 28 mpg — so its fuel-efficiency advantage holds whether you commute in traffic or cover long highway miles.

Powertrain choice: the Audi S6 is recorded with 2 distinct engine configurations (SIDI; Mild Hybrid, SIDI), the BMW 8 Series with 1 (SIDI). Across 10 recorded Audi S6 configurations and 64 for the BMW 8 Series, the wider the engine spread the more the real-world fuel efficiency depends on which version you actually buy, so check the specific model year and drivetrain rather than the headline number.

Drivetrain and class: the Audi S6 is offered with All-Wheel Drive, 4-Wheel Drive, the BMW 8 Series with All-Wheel Drive, Rear-Wheel Drive. All-wheel drive typically costs one to two mpg combined against the same vehicle in front- or rear-wheel drive, which is worth remembering when the gap between these two is small. The EPA classes them as Midsize Cars and Subcompact Cars respectively — the class drives the interior volume, cargo space and passenger space each one is measured against.

Tailpipe emissions: at their cleanest configurations the BMW 8 Series emits 347 g/mile of CO2 versus 408 g/mile for the Audi S6. Emissions track fuel consumption almost exactly, so the cleaner vehicle here is also the cheaper one to fuel.