Mercedes-Benz GLS-Class vs Porsche Cayenne: Specs Compared

Running cost over five years: at the EPA's 15,000-mile-a-year assumption the Porsche Cayenne burns about $3,300 of fuel annually against $3,600 for the Mercedes-Benz GLS-Class. That $300 yearly gap compounds to roughly $1,500 over five years and $2,400 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 Porsche Cayenne leads in both cycles — 21 mpg city and 29 mpg highway against 20 and 24 mpg — so its fuel-efficiency advantage holds whether you commute in traffic or cover long highway miles.

Powertrain choice: the Mercedes-Benz GLS-Class is recorded with 2 distinct engine configurations (SIDI; Mild Hybrid, SIDI), the Porsche Cayenne with 4 (SIDI, SIDI; PHEV, 4.0). Across 35 recorded Mercedes-Benz GLS-Class configurations and 97 for the Porsche Cayenne, 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 Mercedes-Benz GLS-Class is offered with All-Wheel Drive, 4-Wheel Drive, the Porsche Cayenne with All-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 Porsche Cayenne emits 174 g/mile of CO2 versus 414 g/mile for the Mercedes-Benz GLS-Class. Emissions track fuel consumption almost exactly, so the cleaner vehicle here is also the cheaper one to fuel.