Audi RS Q8 vs Mercedes-Benz GLS-Class: Specs Compared

Running cost over five years: at the EPA's 15,000-mile-a-year assumption the Mercedes-Benz GLS-Class burns about $3,600 of fuel annually against $4,750 for the Audi RS Q8. That $1,150 yearly gap compounds to roughly $5,750 over five years and $9,200 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 GLS-Class leads in both cycles — 20 mpg city and 24 mpg highway against 14 and 20 mpg — so its fuel-efficiency advantage holds whether you commute in traffic or cover long highway miles.

Powertrain choice: the Audi RS Q8 is recorded with 1 distinct engine configuration (SIDI; Mild Hybrid), the Mercedes-Benz GLS-Class with 2 (SIDI; Mild Hybrid, SIDI). Across 8 recorded Audi RS Q8 configurations and 35 for the Mercedes-Benz GLS-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 RS Q8 is offered with All-Wheel Drive, the Mercedes-Benz GLS-Class with All-Wheel Drive, 4-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 Standard Sport Utility Vehicle 4WD and Standard Sport Utility Vehicle 4WD 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 GLS-Class emits 414 g/mile of CO2 versus 547 g/mile for the Audi RS Q8. Emissions track fuel consumption almost exactly, so the cleaner vehicle here is also the cheaper one to fuel.