21 MPG combined for the 2025 Mercedes-Benz GLS450 4MATIC 3.0L 6-cyl shows the strong engineering needed to move just under 5,500 pounds of luxury, technology, and genuine seven-passenger capability with this level of refinement. This isn’t a vehicle bought by someone counting pennies at the pump; it’s chosen by individuals who prioritize opulent comfort, a commanding road presence, and Mercedes-Benz’s unwavering commitment to quality. The GLS450 sets the standard for the full-size luxury SUV, offering a driving experience that’s both quiet and surprisingly dynamic for its size. For its clientele, who typically have multiple vehicles and frequently embark on long-distance family journeys, this 21 MPG figure represents a highly acceptable compromise, allowing travel without constant fuel stops, all while enveloped in first-class amenities. Given its role as a premium family hauler and executive transport, the GLS450’s fuel economy shows that even large, powerful luxury SUVs are engineered to be reasonably responsible, a critical consideration in today’s market.

City and highway performance

Looking closer at the EPA estimates, the 2025 GLS450 4MATIC achieves 19 MPG in city driving and 24 MPG on the highway. In urban environments, where stop-and-go traffic and continuous acceleration and braking cycles prevail, the integrated mild-hybrid system, EQ Boost, plays an important role in reaching that 19 MPG figure. This 48-volt system provides a temporary power boost and manages engine start-stop functions with remarkable smoothness, allowing the large GLS to glide away from lights without excessive fuel consumption. The nine-speed automatic transmission, a masterclass in gear management, ensures the engine operates in its most efficient range even during frequent speed changes. On the open road, the GLS450 truly shines, delivering 24 MPG. The 3.0-liter inline-six engine, known for its buttery-smooth power delivery, effortlessly maintains highway speeds, typically operating at low RPMs in higher gears. Aerodynamics, while challenging for a vehicle of this stature, are optimized to minimize drag, contributing to the impressive highway figure. When cruising at optimal speeds, the GLS feels entirely unstressed, a characteristic that buyers expect and appreciate.

Annual fuel cost

The EPA estimates an annual fuel cost of $2,750 for the 2025 Mercedes-Benz GLS450 4MATIC. This figure is based on specific assumptions: 15,000 miles of driving per year, with 45% of that mileage accumulated on highways and 55% in city conditions, applied to national average fuel prices. This is an estimate designed to provide a standardized comparison point across vehicles. Real-world fuel costs inevitably vary based on several factors, including local fuel prices, individual driving habits, and regional traffic conditions. Drivers who spend more time in heavy city traffic, frequently use the vehicle’s full acceleration capabilities, or live in areas with higher fuel costs (particularly premium gasoline, which the GLS450 requires) may see their annual fuel expenditure exceed this estimate. Conversely, those with more highway driving or a light foot on the accelerator might find their costs slightly lower. For the typical GLS buyer, while an acknowledgment of running costs, this $2,750 figure is a manageable aspect of owning an over $80,000 luxury SUV, far overshadowed by the vehicle’s comfort, prestige, and utility.

Real-world expectations

In the real world, the 2025 GLS450 often meets or even slightly exceeds its EPA estimates, particularly on extended highway journeys. Experienced drivers who prioritize smooth acceleration and anticipate traffic will find it’s not difficult to stay within the 21-24 MPG range. Conversely, those who frequently exploit the responsive 375 horsepower and 369 lb-ft of torque, especially during spirited passes or in dense stop-and-go urban gridlock, will inevitably see figures closer to the 19 MPG city rating, or even slightly below it. Hauling a full complement of seven passengers and their luggage, or towing a modest trailer near the GLS450’s 7,700-pound capacity, will also contribute to a decrease in overall fuel economy. The advanced climate control system, with its multi-zone capabilities, can also draw significant power, particularly in extreme temperatures. Ultimately, the GLS450 delivers a consistent experience, its fuel economy is predictable for its class and powertrain, a key factor in luxury vehicle ownership where reliability and consistent performance are critical. Nobody buying a GLS expects Prius-level efficiency, they expect refined power delivery that doesn’t necessitate excessive stops at the gas station.

How it compares

The 2025 Mercedes-Benz GLS450 4MATIC holds its own remarkably well against its direct competitors in the full-size luxury SUV segment. Consider the BMW X7 xDrive40i, which also features a 3.0-liter turbocharged inline-six engine. Its EPA ratings usually hover around 20 MPG combined (19 city/23 highway), essentially on par with the GLS450. The Audi Q7 55 TFSI quattro, with its 3.0-liter V6, typically achieves 20 MPG combined (19 city/22 highway), again, extremely close to the Mercedes. For those who might cross-shop with a Land Rover Range Rover P400, a similar 3.0-liter inline-six with a mild-hybrid system, figures are also in the 20 MPG combined realm (18 city/23 highway). Even the Cadillac Escalade 6.2L V8, which focuses on raw V8 power, lags significantly with a combined 16 MPG (14 city/18 highway). Comparing our GLS450 to smaller luxury SUVs is an apples-to-oranges scenario, the GLS buyer needs the spacious third row and superior overall passenger volume. For all Mercedes Benz fuel economy data, you’ll find similar consistency across their segments. The GLS450’s fuel economy demonstrates that Mercedes-Benz has optimized its powertrain for efficiency without sacrificing the performance and refinement expected from a flagship SUV. For GLS450 MPG across all years, note the gradual improvements achieved through powertrain advancements.

Tips to maximize efficiency

Maintaining proper tire pressure is one of the easiest and most effective ways to preserve the GLS450’s fuel economy. Underinflated tires increase rolling resistance, forcing the engine to work harder. Check your tire pressures regularly, especially before long trips, adhering to the manufacturer’s recommended settings found on the driver’s side door jamb.

Adopt a smooth driving style. Aggressive acceleration and hard braking significantly reduce fuel efficiency by wasting kinetic energy. The GLS450’s turbocharged engine with an electric motor is designed for fluidity; capitalize on this by anticipating traffic, gentle throttle inputs, and coasting to stops where appropriate.

Use the vehicle’s drive modes. While the GLS450 offers dynamic modes, selecting “Comfort” or “Eco” mode optimizes the engine, transmission, and climate control for maximum efficiency. These modes smooth out throttle response and encourage earlier upshifts, actively working to conserve fuel.

Reduce unnecessary weight. While the GLS is a substantial vehicle, every extra pound contributes to fuel consumption. Remove any items from the cargo area that aren’t essential for your journey. Similarly, roof racks and cargo boxes should only be mounted when needed, as they significantly increase aerodynamic drag.

Regular maintenance is critical for optimal fuel efficiency. Adhere to Mercedes-Benz’s recommended service intervals for oil changes, air filter replacement, and spark plug checks. A well-maintained engine runs more efficiently, directly translating to better fuel economy over the long term.