True MPG: least efficient cars revealed

What Car?'s laboratory tests use a real-world driving route to show what fuel economy you can really expect. So, what are the best and worst performing cars?...

Porsche Macan - True MPG logo

So, you've seen the most efficient cars, all of which average more than 55mpg in real-world driving conditions, but which cars use the most fuel?

Here we answer that question and see just what they do deliver if you’re driving gently and sticking to speed limits, but aren’t resorting to any unrealistically slow acceleration or special 'hypermiling' techniques.

The 10 least fuel-efficient cars tested:

Volvo XC40 D4 R-Design front three quarters

True MPG 27.1mpg

We're big fans of this family SUV; it was even our 2018 Car of the Year. However, while this turbocharged 2.0-litre petrol version is nice to drive, a True MPG score of 27.1 makes it significantly harder to recommend.

Read our full Volvo XC40 review >>

9. Mercedes S500

New BMW 7 Series vs Mercedes S-Class

True MPG 26.9mpg

The S-Class has long been one of the best luxury saloons around and is extremely relaxing to drive or be driven in. However, despite featuring mild hybrid technology, the previous-generation S500 version is anything but frugal. A new version has since gone on sale.

Used Land Rover Discovery 4x4 (17-present)

True MPG 26.3mpg

Large, luxurious SUVs aren't an efficient breed, but even by the standards of the class the Land Rover Discovery gulps down a lot of fuel, barely topping 26mpg.

Read our full Land Rover Discovery review >>

=6. Mercedes-AMG GLC 43

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Mercedes-AMG GLC 43 front

True MPG 25.3mpg

If you get your thrills from blasting away from traffic lights and listening to a piercing V6 soundtrack, the GLC 43 is well worth a look. It’s even practical and easy to drive when you’re in family mode. But it's never what you'd call frugal.

Read our full Mercedes GLC review >>

=6. Porsche Macan Turbo Performance Pack

Buy a new Porsche Macan with What Car? >>

BMW M3 vs Porsche Macan Turbo

True MPG 25.3mpg

The Macan Turbo is a rival for the GLC 43, and averaged the same 25.3mpg when we put it through our True MPG test. However, it's since been given a new engine and is the more rewarding car to drive.

Read our full Porsche Macan review >>

5. Mercedes S500 Cabriolet

Mercedes S-Class Cabriolet

True MPG 25.2mpg

Until it was discontinued in 2020, the S-Class Cabriolet was the best luxury drop-top you could buy. However, it was only for those with a big balance, due to its high price and running costs.

Read our full used Mercedes S-Class Cabriolet review >>

4. Audi SQ5

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Audi SQ5

True MPG 24.6mpg

Like the rival GLC 43 and Macan Turbo, the SQ5 is as heavy on fuel as it is light on its feet – or at least it was until Audi swapped the petrol engine for a diesel. Strengths also include a beautifully built interior.

Lexus LC 500 Convertible 2020

True MPG 24.2mpg

With this open-top version of the Lexus LC, you can look forward to turning the heads of other road users as you pass, and breathtaking performance. You can also look forward to visiting the petrol station often, courtesy of this version's 4.0-litre V8 engine.

Read our full Lexus LC review >>

2. Alfa Romeo Giulia Quadrifoglio

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New Alfa Romeo Giulia Quadrifoglio vs BMW M3

True MPG 23.5mpg

Like so many cars in this bottom 10, the Giulia Quadrifoglio is designed for performance rather than efficiency. Indeed, it's a former What Car? Performance Car of the Year, which tells you just how good it is at the things it specialises in.

Read our full Alfa Romeo Giulia Quadrifoglio review >>

1. Audi S8

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Audi S8 2020

True MPG 21.7mpg

It offers savage straight-line performance and is incredibly comfortable, but there's no getting around the fact that this go-faster version of the Audi A8 luxury limousine will be hideously expensive to run. Still, if you can afford to put one on your driveway in the first place, running costs aren't likely to factor among your biggest concerns.

Read our full Audi S8 review >>

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