Audi S8 vs Mercedes-Benz CLS-Class: Specs Compared

Running cost over five years: at the EPA's 15,000-mile-a-year assumption the Mercedes-Benz CLS-Class burns about $2,900 of fuel annually against $3,800 for the Audi S8. That $900 yearly gap compounds to roughly $4,500 over five years and $7,200 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 Mercedes-Benz CLS-Class leads in both cycles — 24 mpg city and 31 mpg highway against 16 and 27 mpg — so its fuel-efficiency advantage holds whether you commute in traffic or cover long highway miles.

Powertrain choice: the Audi S8 is recorded with 2 distinct engine configurations (SIDI; Mild Hybrid, SIDI), the Mercedes-Benz CLS-Class with 2 (SIDI; Mild Hybrid, SIDI). Across 12 recorded Audi S8 configurations and 27 for the Mercedes-Benz CLS-Class, 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 S8 is offered with All-Wheel Drive, the Mercedes-Benz CLS-Class with All-Wheel Drive, 4-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 Large Cars and Compact 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 Mercedes-Benz CLS-Class emits 334 g/mile of CO2 versus 452 g/mile for the Audi S8. Emissions track fuel consumption almost exactly, so the cleaner vehicle here is also the cheaper one to fuel.