16 MPG combined. That’s the fuel economy reality for the 2018 Mercedes-Benz GLS550 4matic. While that number might make hybrid car owners shudder, GLS550 buyers probably aren’t comparing it to a Prius. This SUV is large, luxurious, and powerful, and its gas consumption reflects that.

City and highway performance

The EPA estimates the GLS550 gets 14 MPG in the city and 19 MPG on the highway. The difference highlights a weak point: stop-and-go traffic. The 4.7-liter twin-turbo V8 needs a lot of fuel to move its weight from a standstill. On the open road, the 9-speed automatic transmission helps keep the engine running efficiently. But even at a constant speed, a vehicle this size needs significant energy to overcome wind resistance.

Annual fuel cost

The EPA says the annual fuel cost for the 2018 Mercedes-Benz GLS550 4matic is about $3,600. This is based on driving 15,000 miles a year, with 55% in the city and 45% on the highway, using average national gas prices. It’s a considerable amount, an expense anyone considering this vehicle should keep in mind. Factor it into your budget along with the purchase price and other ownership costs.

Real-world expectations

EPA estimates are a standard way to compare vehicles, but real-world gas mileage can change a lot based on driving habits, traffic, and even the weather. Fast acceleration, hard braking, and long idling will hurt your fuel economy. Drivers in busy cities might see numbers lower than the EPA’s 14 MPG city rating. On the other hand, those who often take long highway trips might get slightly better than the 19 MPG estimate. Tire pressure and car maintenance also matter. The GLS550 also requires premium fuel, which increases the overall cost.

How it compares

The GLS550’s fuel economy is about what you’d expect for a large, powerful luxury SUV. The BMW X7 xDrive50i, with its 4.4-liter V8, gets a combined EPA rating of 17 MPG. The Land Rover Range Rover, also with a supercharged V8, is around 16 MPG combined. Even the Lexus LX 570, known for reliability more than gas mileage, only gets 14 MPG combined. A less powerful GLS450 boasts 20 MPG. These comparisons show that fuel economy isn’t usually the main concern for buyers in this category. Space, performance, and luxury are more important. You can view GLS550 MPG across all years to see if this model year is aligned with others.

Tips to maximize efficiency

The GLS550 isn’t made for optimal fuel efficiency, but drivers can take steps to reduce gas use. Accelerate smoothly and steadily to avoid putting extra strain on the engine. Using cruise control on the highway helps keep a constant speed, which can improve gas mileage.

Make sure tires have the right amount of air, as recommended by the manufacturer. Tires with low air pressure increase rolling resistance, making the engine work harder and burn more fuel.

Remove extra weight from the car by taking out unnecessary items. The lighter the vehicle, the less energy it takes to move it. Also, keep roof racks to a minimum, since they create drag.

Avoid idling for long periods. If you’re going to be stopped for more than a minute, turn off the engine. Modern engines are made to restart quickly and efficiently, and idling uses fuel without moving the car.

Finally, keep the car properly maintained. Regular oil changes, air filter replacements, and spark plug maintenance keep the engine running smoothly and efficiently. Find all Mercedes Benz fuel economy data on this site.