21 MPG combined isn’t going to win any fuel-sipping awards, but for the 2020 Mercedes-Benz GLS450 4matic, it’s an acceptable tradeoff. This vehicle is built for space, comfort, and effortless long-distance cruising, not hypermiling. The GLS450 buyer prioritizes a quiet cabin, reliable power, and the cachet of the three-pointed star over squeezing every last mile from each gallon. Think soccer practice shuttles, ski trips to Vail, and weekend getaways with the extended family. Fuel efficiency is a consideration, not the defining factor.

City and highway performance

The EPA estimates suggest 19 MPG in the city and 23 MPG on the highway. The city figure reflects the GLS450’s weight and the stop-start nature of urban driving. The engine’s mild-hybrid system provides a boost during initial acceleration and helps smooth out transitions, but it can’t completely overcome the demands of hauling over 5,300 pounds around town.

The highway MPG is more representative of the engine’s efficient cruising ability. The 9-speed automatic transmission helps to keep the engine in its sweet spot at higher speeds and contributes to the relatively respectable fuel economy on long journeys. Be aware that these official numbers can vary quite a bit, and drivers with a heavy foot will certainly see their MPG average drop.

Annual fuel cost

The EPA estimates that the annual fuel cost for the 2020 Mercedes-Benz GLS450 4matic will be $2,750. This figure is based on driving 15,000 miles per year, using a national average fuel price. Keep in mind that this is just an average; your actual fuel costs will depend on your driving habits, the type of driving you do (city vs. highway), and the prevailing fuel prices in your area.

If you primarily drive in the city or have a lead foot, expect to spend more; conversely, consistent highway driving at moderate speeds will likely reduce your annual fuel bill. If you are shopping for all Mercedes Benz fuel economy data, make sure you get the right information.

Real-world expectations

While the EPA provides a standardized benchmark, real-world fuel economy often deviates. GLS450 owners frequently report figures slightly below the official estimates, especially in mixed driving conditions. Factors like traffic congestion, weather conditions, tire pressure, and even roof racks can impact mileage.

The GLS450’s 4MATIC all-wheel-drive system enhances safety and traction. It also adds some weight and complexity, which can have a subtle effect on efficiency. Drivers should also be aware that premium fuel is recommended (though not always required), impacting the cost per gallon.

How it compares

Compared to its rivals, the 2020 Mercedes-Benz GLS450 4matic sits roughly in the middle of the pack for fuel economy in its class. The BMW X7 xDrive40i, with its similar turbocharged inline-six engine, achieves an EPA-estimated 21 MPG combined, mirroring the GLS450. The Land Rover Range Rover, especially with a V8 engine, typically delivers significantly lower fuel economy, often landing in the 16-18 MPG range.

The Lexus LX 570, with its naturally aspirated V8, is even less efficient, barely cracking 15 MPG. A more efficient option might be the Acura MDX, especially in its hybrid variant, which can consistently break 25 MPG combined, but it lacks the GLS450’s prestige and spaciousness. For buyers considering GLS450 MPG across all years, it’s crucial to compare the specific engine configurations, as fuel economy can vary within the GLS range.

Tips to maximize efficiency

Use the GLS450’s driving modes. The “Comfort” or “Eco” mode optimizes throttle response and transmission behavior for fuel efficiency. Avoid aggressive acceleration and braking, as these actions consume more fuel. Gradual increases in speed and smooth deceleration allow the engine to operate more efficiently.

Maintain proper tire inflation. Underinflated tires increase rolling resistance, forcing the engine to work harder and reducing fuel economy. Check your tire pressure regularly and inflate them to the recommended levels found on the doorjamb sticker. This simple step can make a noticeable difference over time.

Reduce unnecessary weight. Carrying extra cargo in the trunk or on the roof creates additional drag and reduces fuel efficiency. Remove any items you don’t need on a regular basis. Even small weight reductions can add up, particularly on longer trips. This is especially true if you tend to leave heavy items in the spacious third row.

Minimize idling. Avoid idling for extended periods, as this consumes fuel without covering any distance. If you anticipate being stopped for more than a minute, turn off the engine. The GLS450’s start/stop system is designed to help with this, but only activates in certain conditions; manual intervention can often further improve efficiency.