21 MPG combined makes the 2026 Mercedes-Benz GLS450 4MATIC 3.0L 6-cyl a remarkably efficient full-size luxury SUV. This is especially true considering its 5,500-pound curb weight, all-wheel-drive system, and the sheer volume of luxury and technology it carries. This isn’t a vehicle bought for outright fuel efficiency, but rather one where efficiency becomes a pleasant bonus, allowing its target buyer to enjoy long-distance comfort and capability without constant fuel stops. The GLS450 is the definitive German executive hauler, designed for families who demand prestige, space, and a refined driving experience, often covering significant highway miles between estates or vacation homes. Its fuel economy isn’t the primary driver of purchase, but it underscores Mercedes-Benz’s commitment to delivering a well-rounded package, marrying opulence with a measure of lower fuel costs.

City and highway performance

Diving deeper into the EPA figures confirms the GLS450’s balanced approach: 19 MPG in the city and 24 MPG on the highway. The city figure, at 19 MPG, is a commendable achievement for a vehicle of this size and capability. Stop-and-go traffic, with its frequent acceleration and braking, typically penalizes heavy vehicles significantly more. The mild-hybrid EQ Boost system, integrated with the 3.0L turbocharged inline-six engine, plays a crucial role here, smoothly assisting acceleration and enabling a refined start/stop function that conserves fuel at idle. The 9-speed automatic transmission also ensures the engine operates in its most efficient range, even at lower city speeds. On the open road, the 24 MPG highway figure is where the GLS450 truly shines and where its primary owners will see the most benefit. Long highway cruises are the GLS’s natural habitat. The smooth, torquey inline-six, combined with the extended gearing of the 9-speed transmission and aerodynamic design, allows the engine to loaf at low RPMs, minimizing fuel consumption while maintaining effortless cruising ability. This makes it an ideal choice for road trips or for those with longer commutes that heavily favor highway driving, reducing the frequency of stops and enhancing the overall premium travel experience.

Annual fuel cost

The EPA estimates an annual fuel cost of $2,750 for the 2026 Mercedes-Benz GLS450 4MATIC 3.0L 6-cyl. This figure is determined by calculating 15,000 miles of annual driving, split between city and highway driving, using national average fuel prices for premium gasoline. For the high-net-worth individual or family considering the GLS450, this annual expenditure is often seen as a minor operating cost relative to the vehicle’s purchase price and overall maintenance. What it does highlight, however, is the predictability. Knowing this approximate annual cost allows owners to budget for their luxury vehicle ownership experience with greater clarity. It’s a transparent illustration of the running costs, reinforcing the idea that while it’s a large luxury SUV, its fuel consumption is managed to a reasonable level within its segment, preventing unexpected financial surprises at the pump. This $2,750 figure reflects a compromise that Mercedes-Benz has engineered, offering strong performance and significant luxury without presenting an exorbitant yearly fuel bill.

Real-world expectations

In the real world, the 2026 GLS450 4MATIC’s fuel economy will largely depend on driving habits and conditions. Drivers who frequently exploit the responsive turbocharged engine and its ample torque will naturally see figures closer to the 19 MPG city rating, or even slightly below in particularly aggressive urban driving. The subtle but effective mild-hybrid system, however, does much to mitigate this. On the other hand, the hallmark GLS driver, one who appreciates a smooth, unhurried pace on highways and maintains consistent speeds, can expect to meet or even slightly exceed the 24 MPG highway rating. Factors like tire pressure, cargo load, and frequent use of climate control will also influence the outcome. For instance, hauling a full complement of seven passengers and their luggage will inevitably increase fuel consumption. Colder climates, requiring longer warm-up times and increased accessory use, can also slightly depress figures. However, the core character of the GLS450, a refined, comfortable cruiser, tends to encourage a driving style conducive to achieving its rated highway efficiency. Owners buy this vehicle for prestige, comfort, and space, not primarily for its fuel economy, but its efficiency certainly adds to its appeal as a well-engineered luxury vehicle capable of long journeys without undue penalty.

How it compares

Comparing the 2026 Mercedes-Benz GLS450 4MATIC to its immediate rivals reveals its competitive standing in terms of fuel efficiency. The GLS450, with its 21 MPG combined (19 city/24 highway), stacks up well against key competitors. Take, for instance, the BMW X7 xDrive40i, which is typically rated at 22 MPG combined (20 city/24 highway). This indicates a very close performance, with the X7 gaining a marginal advantage in city driving but matching the GLS on the highway. Then there’s the Audi Q7 45 TFSI, which often sees ratings around 21 MPG combined (19 city/24 highway), essentially mirroring the GLS450’s figures precisely. For those considering the Cadillac Escalade 6.2L V8, the contrast is stark. The Escalade 4WD with its larger V8 usually achieves around 16 MPG combined (14 city/18 highway), making the GLS450 a significantly more efficient choice for buyers prioritizing fuel stops. Even the Lexus LX 600, with its twin-turbo V6, typically comes in lower, around 19 MPG combined (17 city/22 highway). This comparison clearly demonstrates that the GLS450’s 3.0L inline-six, combined with its mild-hybrid system and advanced transmission, positions it at the leading edge of fuel efficiency within the large, three-row luxury SUV segment, particularly when compared to non-hybrid offerings. The specific buyers considering a GLS are looking for a blend of luxury, capability, and modern engineering, and its competitive MPG aligns perfectly with this expectation, offering a good alternative to thirstier V8 options while maintaining a premium driving experience. You can review all Mercedes Benz fuel economy data on our site, including GLS450 MPG across all years.

Tips to maximize efficiency

Maintain proper tire pressure, as underinflated tires significantly increase rolling resistance and reduce fuel economy. The GLS450 features a Tire Pressure Monitoring System (TPMS), so heed its warnings and check pressures regularly, especially before long trips, to optimize efficiency and safety.

Use the vehicle’s drive modes effectively, “Eco” mode, specifically engineered to optimize efficiency, adjusts throttle response, transmission shift points, and climate control operation to minimize fuel consumption. For city driving, this can make a noticeable difference.

Practice smooth driving habits, gentle acceleration, anticipating traffic, and coasting to stops whenever safe and possible, rather than sharp braking and rapid acceleration. The GLS450’s smooth powertrain is designed for this type of relaxed driving, which also inherently improves fuel economy.

Minimize unnecessary weight. While the GLS450 is a large vehicle, removing heavy items from the trunk or roof rack when not needed can incrementally improve efficiency by reducing the burden on the powerful 3.0L engine.