15 MPG combined isn’t just a number. For the 2025 Mercedes-AMG GLS63 4MATIC+ 4.0L V8, it means a vehicle not focused on mainstream efficiency. This luxury SUV prioritizes performance and presence. This is like a first-class ticket, where comfort and speed are important, and the fuel cost is simply part of the experience. Buyers of this AMG don’t compare it against frugal hybrids or sensible crossovers. They want uncompromised power, a commanding driving position, and a cabin that rivals private jets. The GLS63’s goal is to move its occupants with astonishing speed and undeniable style, making its fuel consumption a secondary, almost irrelevant, consideration for its audience.

City and highway performance

The EPA figures for the 2025 Mercedes-AMG GLS63 4MATIC+ show 14 MPG in city driving and 18 MPG on the highway. These numbers fit the vehicle’s character. The 4.0L twin-turbocharged V8, with Mercedes-Benz’s EQ Boost mild-hybrid system, is a powerful engine, producing 603 horsepower and 627 lb-ft of torque. In city traffic, that immense power is always ready, requiring frequent throttle input for effortless acceleration and maneuvering. The GLS63’s substantial weight, along with stop-and-go driving, affects city fuel economy. The 9-speed automatic transmission, while smooth and intelligent, manages this power.

On the highway, sustained speeds allow the engine to operate within more efficient ranges, so the GLS63 improves to an 18 MPG rating. This isn’t thrifty, but it shows the engine’s ability to cruise comfortably at lower RPMs once at speed. The aerodynamic profile, optimized for an SUV of its size, still creates significant drag. However, the exact luxury of highway driving in a GLS63 is its ability to cover long distances with unwavering stability, comfort, and immediate power for effortless overtakes. Drivers seeking an AMG GLS63 are primarily interested in how quickly it reaches cruising speed and how quietly it maintains it, not how many sips of premium unleaded it takes to do so. For those interested in more details regarding the performance and efficiency of other AMG models, explore AMG MPG across all years.

Annual fuel cost

The EPA estimates an annual fuel cost of $3,850 for the 2025 Mercedes-AMG GLS63. This figure, calculated based on 15,000 miles of driving per year at national average fuel prices, shows the operational expense of owning such a high-performance luxury SUV. It’s important for potential owners to understand this is a realistic projection of their yearly fuel expenditure. For a vehicle with an MSRP likely approaching or exceeding $140,000, paying nearly four thousand dollars annually for fuel is in line with the overall cost of ownership. The buyer of a GLS63 isn’t surprised or deterred by this figure; it’s simply another line item in the budget of a luxury lifestyle. This cost is for the powerful, premium fuel-hungry engine that provides the vehicle’s exhilarating performance and the exclusive experience for which customers choose an AMG.

Real-world expectations

In real-world driving, owners of the 2025 Mercedes-AMG GLS63 4MATIC+ should expect fuel economy figures similar to, or potentially slightly below, the EPA estimates, depending on their driving style. The thrill of the 603-horsepower V8 is a temptation for many owners, and frequently using that power will lead to lower MPG. Aggressive acceleration, sustained high speeds, and frequent use of “Sport+” driving modes will push consumption closer to the city figure, even outside urban areas. Conversely, a disciplined driver using comfort modes, gentle acceleration, and adhering strictly to speed limits on highway journeys might occasionally see numbers approaching the upper end of the 18 MPG highway estimate.

However, optimizing fuel economy is typically not a primary concern for the GLS63 buyer. Their focus is on the acceleration, the exhaust note, and the commanding presence this vehicle offers. The real-world expectation is less about saving a gallon, and more about the instant gratification and effortless performance that define the AMG experience. Any attempts to hyper-mile this vehicle would miss the point of its existence. It’s designed to be driven, and driven enthusiastically, making its fuel consumption a byproduct of its performance capabilities, not a metric to be meticulously managed.

How it compares

When placed alongside its direct competitors, the 2025 Mercedes-AMG GLS63’s 15 MPG combined rating is where one would expect in the ultra-luxury performance SUV segment. Consider the BMW X7 M60i, a rival with a 4.4L twin-turbo V8, which achieves 18 MPG combined (16 city/21 highway). While seemingly better on paper, the X7 M60i, with its 523 horsepower, is considerably less powerful than the GLS63. For a closer power comparison, the Alpina XB7, from the X7, boasts 630 horsepower from its 4.4L V8 and delivers an identical 18 MPG combined (16 city/21 highway), showing BMW’s efficiency more effectively at higher horsepower outputs.

Then there’s the Audi RS Q8, powered by a 4.0L twin-turbo V8 producing 591 horsepower, which achieves 16 MPG combined (15 city/20 highway). This is marginally better but again, slightly down on horsepower. The Porsche Cayenne Turbo E-Hybrid, with its plug-in hybrid powertrain, offers a remarkable 46 MPGe combined but also generates 729 horsepower, though its gasoline-only combined MPG is closer to 18 MPG (15 city/20 highway). The Cayenne’s hybrid nature offers a different choice. For more information on other luxury vehicles, check out all Mercedes Benz fuel economy data.

The GLS63 competes fiercely. Its performance figures are among the highest out there, and that requires fuel. Buyers choosing the AMG GLS63 are making a conscious decision for peak Mercedes-AMG performance and luxury, where a few MPG difference against rivals doesn’t matter compared to the driving experience, brand cachet, and the audacity of its power delivery.

Tips to maximize efficiency

While maximizing efficiency isn’t the primary goal for most GLS63 owners, some habits can still make a marginal difference. Engaging the “Comfort” driving mode will soften throttle response and shift points, prompting the 9-speed automatic transmission to upshift earlier, keeping the powerful V8 in lower, more fuel-efficient RPM ranges. This mode also ensures the EQ Boost mild-hybrid system is used to its full potential for energy recuperation and assistance.

Practicing smooth acceleration and gentle braking is another effective strategy. Avoiding abrupt stops and starts allows the mild-hybrid system to recover more kinetic energy, which can then be used to assist the engine during light acceleration, reducing the direct load on the V8 and conserving fuel.

Maintaining proper tire pressure is often overlooked but critical for any vehicle’s efficiency. Incorrectly inflated tires increase rolling resistance, forcing the engine to work harder. Regularly checking and adjusting the tire pressure to the manufacturer’s recommended levels ensures optimal contact and reduces unnecessary drag.

For journeys that involve significant highway cruising, using the adaptive cruise control system can help. By maintaining a consistent speed and automatically adjusting to traffic flow, the system minimizes unnecessary acceleration and deceleration, which are significant fuel consumers, particularly with such a powerful engine.

Finally, minimizing unnecessary weight in the vehicle can provide a small but noticeable improvement. While the GLS63 is inherently heavy, removing any non-essential items from the cargo area reduces the load the engine has to move, thereby slightly lessening its fuel demands.