Parkers overall rating: 3.1 out of 5 3.1

Miles per pound (mpp) Miles per pound (mpp)

Petrol engines 2.5 - 2.6 mpp
Diesel engines 3.6 - 3.8 mpp
Low figures relate to the least economical version; high to the most economical. Based on WLTP combined fuel economy for versions of this car made since September 2017 only, and typical current fuel or electricity costs.

Fuel economy

Petrol engines 21.1 - 22.1 mpg
Diesel engines 31.7 - 32.8 mpg
  • Diesel the best performer for fuel consumption
  • Petrols are very thirsty
  • Unlikely to be cheap to maintain

If you don’t want your GLS to be ruinously expensive to run, then stick with the diesel-drinking GLS 400 d. Officially it’s capable of low-30s mpg under the more recent WLTP method of fuel efficiency testing that is designed to better replicate real-world driving.

Our experiences suggest that this is about right, too – we averaged 30.0mpg and frequently saw 36-37mpg on steady motorway runs. Not too bad at all.

Grey 2020 Mercedes-Benz GLS 400 d rear badge detail

At the opposite end of the scale are the AMG and Maybach models, both powered by a 4.0-litre petrol engine. Thanks to being (a little) lighter, the more powerful AMG GLS 63 is ever so slightly more economical at around 22mpg, compared with the Maybach GLS 600’s claim of just over 21mpg.

Such differences are nuanced and in the real-world, because the AMG encourages you to drive harder, it’s likely to be the champion guzzler. Don’t expect either to achieve above 20mpg with any great frequency, though.

Not very eco-friendly, then?

All GLS models emit well over 200g/km, with the V8 versions hovering around 300g/km. Not only are all very expensive for first year VED car tax, they all slot into the 37% bracket for Benefit-in-Kind (BiK) company car tax.

Other running costs for the GLS will also be expensive, not least servicing, tyres – the minimum wheel size is 22 inches, don’t forget – and similarly brakes, particularly for the AMG models. This is not a car that can be run on a budget and trying to do so will only harm the Mercedes and its resale value.

Is it reliable?

The GLS is covered by Mercedes’ standard three-year/60,000-mile warranty if anything goes wrong. The previous model was the subject of just one recall regarding the power steering, and no others.

This latest GLS is all-new however, with new components shared with the latest GLE. There are a lot of systems to go wrong, but it all feels solidly put together and would have been tested thoroughly to put up with the rigours of life as a luxury SUV.

So far there have been no official recalls actioned by the DVSA, so a sound start.

Red and grey 2021 Mercedes-Maybach GLS 600 side elevation

Ongoing running costs

Road tax (12 months) £520
Insurance group 47 - 50
How much is it to insure?