True MPG: Most and least efficient luxury cars and SUVs

What Car?'s True MPG tests show what fuel economy you can really expect from a car. Here, we reveal the best and worst-performing luxury models we've ever tested...

BMW X5 with True MPG logo

The official MPG figures published in car sales brochures can tempt you into buying a certain model, but those results are usually misleading and you probably won't be able to match the figures when you take the car home. So, to show you the sort of fuel economy you can expect in real-world use, What Car? does its own True MPG tests. 

Here, we're counting down the top 10 luxury cars and luxury SUVs. The cars in these classes are all highly desirable and sought out for their sumptuous interiors, high levels of comfort and supreme refinement. In this class, buyers' expectations are high but, despite the obvious opulence, decent fuel economy is still an important factor.

Here, we reveal which models cost the most – and the least – to run.

The most fuel-efficient luxury car or luxury SUV: Mercedes E-Class

Mercedes E-Class front right tracking shot

True MPG Average 44.8mpg | Town 34.7mpg | Motorway 41.4mpg | Rural 59.2mpg

The E-Class is very well equipped and available with a great range of engines, from fuel-sipping diesels and punchy petrols to a tax-efficient plug-in hybrid (PHEV). It's the E220d diesel that wins top honours in the luxury car class for frugality, though. It's not just good for fuel economy, either – it also has plenty of oomph, and is impressively quiet and comfortable on a motorway. Meanwhile, the classy interior is suitably upmarket and decently spacious. A facelifted version of this car is now on sale, but should be just as efficient.

Read our full Mercedes E-Class review or see new Mercedes E-Class deals >>

Read on to find out how we find your car's True MPG, and see more luxury cars and luxury SUVs that performed well in our tests, as well as the model that will cost you the most to run.

How we test for a car's True MPG

Our True MPG tests are carried out on a rolling road under laboratory conditions. That means variables such as weather or traffic conditions don't affect our results, making our test a useful comparison tool. The routes the cars take are based on a realistic mix of roads.

Every car we test is weighed and has its tyre pressures checked, then we hook up an exhaust connection to measure the car's emissions. The car's climate control is set to 21C, or if it has manual air conditioning, the temperature is set to its midway point, and the fan speed to its lowest setting. We turn off the headlights and don't use other electrical equipment, such as heated seats or the stereo.

In the test, we sample each car's tailpipe emissions every second. The True MPG scores you see in this story are calculated from an average of those results.

The best of the rest: luxury cars and luxury SUVs

2. BMW 5 Series

BMW 5 Series front cornering

True MPG: 43.5mpg

We're big fans of the 5 Series – indeed, it's a former What Car? Car of the Year and remains a top choice in the luxury car market. As well as offering refinement, practicality and comfort galore, it's also efficient, especially if you opt for the 2.0-litre diesel engine in this 520d model. In our real-world tests, it returned an impressive 39.9mpg on a motorway, and up to 57.2mpg on country roads. If you're looking for a luxury car that won't break the bank to run but isn't a PHEV, you can do no better.

Read our full BMW 5 Series review or see new BMW 5 Series deals >>

3. Volvo S90

Volvo S90 2021 front right tracking

True MPG: 39.9mpg

The S90 is spacious and comfortable, and comes with a huge array of standard kit to make your life easier. This D4 2.0-litre diesel is no longer available to order because the S90 is sold new only as a plug-in hybrid now, but prices for an early version from around 2016 start at just £14,000 (see used Volvo cars for sale for examples).

Read our full Volvo S90 review or see new Volvo S90 deals >>

4. Mercedes S-Class

Mercedes-Benz S-Class S560e front three-quarters shot

True MPG: 35.1

If you want refinement, comfort and even semi-sensible running costs, few cars can beat the previous-generation S-Class. As with any Mercedes S-Class, the 258bhp diesel engine fitted to this model is hushed at speed, but produces enough power to make acceleration effortless in almost any scenario. It's also fairly efficient, returning 33.2mpg on a motorway in our hands, and 27.0mpg around town. The best news is that prices start from just £15,000.

Read our full 2014-2020 Mercedes S-Class review or find used Mercedes cars for sale >>

5. BMW X5

BMW X5 front cornering

True MPG: 34.1

The X5 offers comfort, refinement and the best infotainment system around. This version is powered by a 282bhp 3.0-litre diesel engine and is badged xDrive30d. It offers punchy performance from low down in its rev range and, thanks to a quick-shifting automatic gearbox, doesn't struggle when you've filled it to the rafters. It managed 25.1mpg around town in our tests, and 31.7mpg on a motorway.

Read our full BMW X5 review or see new BMW X5 deals >>

6. Audi Q7

Audi Q7 2021 front cornering shot

True MPG: 34.0

The 272bhp 3.0-litre diesel engine we rank here is no longer available to order in a new Q7, but there are plenty of examples available on the used market, and prices aren't as high as you might think (see used Audi cars for sale for examples). No matter which version you go for, you'll enjoy a smooth and powerful engine, plus superb interior quality and a boot that can swallow everything you choose to take with you – even if it includes the kitchen sink.

Read our full Audi Q7 review or see new Audi Q7 deals >>

7. Volvo XC90

Volvo XC90 2022 front cornering

True MPG: 33.9

This version of the XC90 luxury SUV is powered by a 2.0-litre diesel engine with mild-hybrid assistance. It works well mostly, although if you're fully loaded with people and luggage, you'll need to put your foot down to build speed quickly. We haven't True MPG tested the T8 PHEV model, but it can officially cover up to 42 miles on electric power alone.

Read our full Volvo XC90 review or see new Volvo XC90 deals >>

8. BMW X7

BMW X7 2021 front cornering shot

True MPG: 31.7

The X7 is the largest and most luxurious SUV BMW makes, and impresses with its spacious and practical interior, its class-leading infotainment system, and its refinement. The 3.0-litre diesel engine that kicks off the range has 347bhp and can hit 60mph in a swift 5.9sec – making it faster than most rivals – yet is also smooth and hushed. It returned upwards of 45mpg on country roads, 33.6mpg on a motorway, but just 18.4mpg around town.

Read our full BMW X7 review or see new BMW X7 deals >> 

9. Lexus RX L

Lexus RX L front right tracking shot

True MPG: 30.8

The RX L has a bit of an advantage over most models on this list because it's a hybrid car. In our urban tests, it managed 45.2mpg, but that fell to 23.7mpg on a motorway. We like the model's long list of standard equipment and good interior build quality, but a fiddly infotainment system and the fact that some rivals are better to drive count against it.

Read our full Lexus RX L review or see new Lexus car deals >>

10. Genesis G80

Genesis G80 front right tracking shot

True MPG: 28.9

Genesis is the new kid on the block in the world of luxury cars, but if you're looking for something a bit leftfield, the 300bhp 2.5-litre petrol engine fitted to this version might catch your eye. It's quick (0-62mph takes just 6.0sec), but running costs can start to mount if you drive in town a lot. This version returned 19.9mpg in our urban driving tests, rising to 28.6mpg on a motorway.

Read our full Genesis G80 review or see new Genesis G80 deals >>

And the least efficient luxury car or luxury SUV

We've listed the cars that will cost you the least in fuel bills in the luxury car and luxury SUV classes, but what about the car that will cost you the most to run? Here's the model that performed the worst in our real-world tests.

Audi S8

Audi S8 2022 front cornering shot

True MPG: 21.7mpg

This go-faster version of the A8 luxury limo gets a 563bhp 4.0-litre V8 petrol engine capable of launching you to 62mph in just 3.8sec. Those are impressive statistics, and as well as offering driving thrills, this S8 is comfortable to be driven in, with incredible refinement and a plush interior. Just be sure you'll be able to afford to run it after you've bought it.

Read our full Audi S8 review or see new Audi S8 deals >>

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