Owners report 24.6 mpg from a Mercedes-Benz GLS, about 73% of the official figure. On its NEDC-tested engines that is 73%, worse than typical: the median NEDC-tested car in this 8,216-engine dataset returns 82%. The tables below give the figure for every engine and generation we hold. Add your own at the bottom and the averages get better for the next buyer.
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Check a Mercedes-Benz GLS advert (free) →| Engine | Official (NEDC) | Official (WLTP) | Real MPG | % of official | Owners report |
|---|---|---|---|---|---|
| GL 350 BlueTec | 36.2 | – | 27.5 | 76% | 22.0–33.4 |
| GL 350 CDI | 36.2 | – | 26.5 | 73% | – |
| GL 63 AMG | 23.0 | – | – | – | – |
| GLS 350 d | 35.3–37.2 | – | 26.3 | 72% | 24.5–28.5 |
| GLS 400 | 26.2 | – | – | – | – |
| GLS 63 AMG | 20.2 | – | 14.0 | 69% | 12.0–16.0 |
| Engine | Official (NEDC) | Official (WLTP) | Real MPG | % of official | Owners report |
|---|---|---|---|---|---|
| GLS 400 d | – | 32.1–32.8 | – | – | – |
| GLS 600 Maybach | – | 21.1 | – | – | – |
| GLS 63 AMG | – | 22.1 | – | – | – |
All figures in miles per gallon (UK). “Owners report” is the spread of individual submissions for that engine.
What does yours actually do? Read it off the trip computer over a full tank or work it out from litres and miles. No postcode, no sign-up. The more people add, the better the averages get, and this page stays free.
Owners report an average of 24.6 mpg across all Mercedes-Benz GLS engines with data, about 73% of the official combined figure. The engine tables on this page give the figure for each engine and generation.
Official figures come from a laboratory test cycle, not the road. Cold starts, short trips, hills, load, tyres and driving style all cost fuel the test does not see. A gap of 10 to 30 per cent is normal; a much bigger gap on one engine usually points at a fault, a heavy right foot, or a diesel that never gets warm.
The site closed in August 2026 and its Real MPG section went with it. This page is where the Mercedes-Benz GLS figures now live: rebuilt from the archived dataset, with the official figures kept alongside, and reopened for new submissions.
Looking at a Mercedes-Benz GLS right now? Check the advert before you go and see it.
If you used the Honest John Real MPG section before the site closed in 2026, this is where the Mercedes-Benz GLS figures now live. The owner-reported averages above were rebuilt from the archived dataset (archived page, 2025-08) alongside the official NEDC and WLTP figures and new submissions from CarAdCheck readers, and the section is open so they keep improving. Real-world figures also feed the running-cost estimate in our free advert check.
CarAdCheck is not affiliated with Honest John or Volkswagen Financial Services. How we rebuilt Real MPG.
Fuel economy is one line on the Mercedes-Benz GLS running-cost sheet. These guides cover the checks that stop you buying the wrong one.