Real MPG: most economical diesel cars - and the least

Diesel cars might not be fashionable, but if you do big miles and want small fuel bills they still make huge sense. Here are the most economical – and the ones which will cost you the most to run...

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by
Stuart Milne
Updated20 February 2024

In the past, drivers looking to eke out the maximum number of miles per gallon would often choose a diesel car. But with pressures of local air pollution and the rise of the London ULEZ and other clean air zones, they're falling out of favour as new-car purchases.

But that's not to say you should overlook them because the appeal of low running costs and low CO2 emissions remains as strong as ever, which is why we're running down the most efficient diesel cars, following results published in our fully independent Real MPG tests.

These tests reveal what sort of fuel economy you can expect in the real world, rather than quoting the official government MPG figures that are published on manufacturers' websites.

Real MPG: most efficient diesel cars

Topping the list of the most economical diesel cars is the Skoda Octavia 2.0 TDI, which in our laboratory and in the hands of our expert testers achieved an impressive 57.9mpg. That's despite it being a spacious, practical family car.

Choosing a diesel car right now has another benefit besides great economy, too. Because they're not as fashionable as they once were, there are plenty of diesel car deals to be had out there, particularly through our free New Car Deals service.


How we test for a car's Real MPG

We carry out our Real MPG tests using a rolling road, with strict laboratory conditions in force. This way, such variables as weather and traffic conditions have no effect on our results – making them repeatable – but the test is based on a real-world route.

Every test car is weighed and we check that the tyre pressures match the manufacturer's recommendation, and we install an exhaust connection so the car's emissions can be measured. The climate control system is set to a standard 21deg C, or – on cars with manual air conditioning – the temperature dial is set to its midway point and the fan speed on its lowest setting. We're also sure to turn off the headlights as well as any other electrical equipment: heated seats or the stereo, for instance.

During testing, each car's tailpipe emissions are sampled every second. The Real MPG scores you see in this story are calculated from an average of those results.

Find out more about how we test for Real MPG >>

Our pick: 1.5 TSI 150 SE L 5dr

0-62mph: 8.5 sec
MPG/range: 53.3mpg
CO2 emissions: 121g/km
Seats: 5
Boot: 600 litres
Insurance group: 21P
Reliability
Safety
Costs
Quality
Performance

Strengths

  • Plush interior
  • Huge boot
  • Frugal engines

Weaknesses

  • Rivals are sharper to drive
  • Touchscreen can be tricky to use on the move
  • Currently no plug-in hybrid option

Real MPG Average 57.9mpg | Town 50.5mpg | Motorway 52.1mpg | Rural 72.6mpg

As if the Skoda Octavia, the thoroughly sensible and highly regarded family car, needed another string to its bow, it takes the crown as the most fuel-efficient diesel car we've ever tested. This is on top of it having terrifically spacious rear seats and a simply enormous boot, as well as interior quality that wouldn't be out of place in a much more expensive car. The 115bhp 2.0-litre diesel engine has plenty of low-down shove, too, which helps to make it relaxing to drive.

In pretty much every economy test, the Octavia impressed, but it was the mighty 72.6mpg figure on rural roads that really stood out. With the exception of the rural figure the Vauxhall Astra (below) achieved, no diesel car on our list recorded more miles per gallon.

Read our full Skoda Octavia review

Our pick: 1.2 Turbo 130 GS 5dr

0-62mph: 9.7 sec
MPG/range: 52.3mpg
CO2 emissions: 123g/km
Seats: 5
Boot: 422 litres
Insurance group: 19E

Strengths

  • Spacious interior
  • Relatively cheap to buy
  • Well equipped

Weaknesses

  • Vague steering
  • Diesels can be noisy
  • Low-speed ride can be fidgety
  • Reliability mixed

Real MPG Average 56.3mpg | Town 46.4mpg | Motorway 50.7mpg | Rural 73.7mpg

This model from the previous-generation Vauxhall Astra range is the second most efficient diesel-engined car we have ever tested, managing more than 56mpg in real-world conditions and an astonishing 73.7mpg on country roads. When it was new, the Astra impressed with plenty of interior space, a good amount of standard equipment and attractively low prices. And having been replaced with an all-new model, the 2015-2021 Astra represents terrific value as a used-car buy.

Read our full used Vauxhall Astra (2015-2021) review

Strengths

  • Good to drive
  • Well equipped
  • Cheap to buy and run

Weaknesses

  • Firm ride
  • Not as refined as some rivals
  • Bland interior

Real MPG Average 56.0mpg | Town 46.3mpg | Motorway 50.9mpg | Rural 71.7mpg

The previous-generation Seat Leon might have discontinued several years ago, but it remains an appealing family hatchback. It's better to drive than the marginally more efficient Astra, but still offers plenty of standard equipment. There's more wind and road noise than you'll find in some rivals, but it's an interesting alternative to many of the class leaders. The Ecomotive version that performed so well in our tests received a raft of tweaks to save fuel, but you can expect similar economy from other models in the range. 

Read our full used Seat Leon (2013-2020) review

Strengths

  • Spacious interior
  • Bigger boot than sibling Nissan Qashqai
  • Quiet petrol engines

Weaknesses

  • So-so quality
  • Grabby brakes
  • Choppy ride on big alloys

Real MPG Average 55.2mpg | Town 50.0mpg | Motorway 48.8mpg | Rural 69.1mpg

The Renault Kadjar is proof that you can buy a family-sized SUV that can return stellar real-world fuel economy; in this case, more than 55mpg which makes it the most frugal family SUV we've ever tested. We like the smooth diesel engine, which is reasonably punchy despite a relatively small 113bhp power output. We also like it's spacious inside, and that its boot is larger than the more well-known Nissan Qashqai which it shares its underpinnings with. 

Read our full used Renault Kadjar review

Driving
Interior
Practicality
Buying & Owning

Strengths

  • Hugely spacious boot and interior
  • Minimal wind noise
  • Well priced, and hybrid makes a cheap company car

Weaknesses

  • Hybrid isn’t as practical as other versions
  • Interior quality disappoints in places
  • Some estates are more fun to drive

Real MPG Average 54.8mpg | Town 45.8mpg | Motorway 49.5mpg | Rural 70.4mpg

What's not to like about the Skoda Superb Estate? Not only is it massive inside, so it can take all of your passengers, plus their luggage, and still come asking for more, but it's also comfortable and good to drive. And if you opt for this 2.0-litre diesel engine, it will even be ruthlessly economical, so you won't spend much time (or money) filling up. It's a no-lose situation if ever we saw one.

Read our full Skoda Superb Estate review

Strengths

  • Comfortable ride
  • Engaging to drive
  • Huge boot

Weaknesses

  • Cheap-feeling plastics inside
  • Fiddly touchscreen
  • Some rivals offer better value

Real MPG Average 53.7mpg | Town 47.7mpg | Motorway 47.0mpg | Rural 66.2mpg

After three decades, the venerable Ford Mondeo has now been discontinued – but a good used example is well worth seeking out. Not only is it spacious and good to drive, blending agile handling and a comfortable ride, it was named most reliable executive car in our most recent reliability survey. While our reviewers prefer the larger 2.0-litre TDCI diesel, it's the smaller 1.5-litre engine that is the real-world economy champion.

Read our full used Ford Mondeo (2014-2022) review

Strengths

  • Plenty of kit
  • Economical engines
  • Low wind noise at speed

Weaknesses

  • Tight rear head room
  • So-so handling
  • Rivals have bigger boots

Real MPG Average 53.3mpg | Town 46.4mpg | Motorway 47.8mpg | Rural 67.2mpg

Like the Ford Mondeo, the Vauxhall Insignia is no longer sold new, but it makes an interesting alternative executive car choice and costs a lot less than an Audi A4 or BMW 3 Series of similar age. A 1.5-litre diesel engine sounds a little small for a car of this size, but it's far from out of its depth, as those economy figures suggest. Some rivals are more fun to drive, but the Insignia is a comfortable machine in which to clock up big mileages.

Read our full used Vauxhall Insignia (2017-2022) review

Our pick: 1.0 EcoBoost Hybrid mHEV Titanium 5dr

0-62mph: 10.2 sec
MPG/range: 54.3mpg
CO2 emissions: 118g/km
Seats: 5
Insurance group: 15E
Reliability
Safety
Costs
Quality
Performance

Strengths

  • Great handling
  • Well equipped
  • Roomy rear seats

Weaknesses

  • Not that cheap to buy
  • Low-rent interior
  • Octavia has a much bigger boot

Real MPG Average 52.4mpg | Town 45.2mpg | Motorway 47.0mpg | Rural 66.2mpg

The Ford Focus is a household name, but there's more reason to choose the big-selling Ford than just popularity. If you go for the 1.5-litre diesel engine on offer, not only will you have plenty of pulling power at your disposal, but it's also a very economical choice on any kind of journey. The Focus remains one of the best-handling family hatchbacks, especially in more sporty ST-Line guise. But regardless of trim, it's well equipped and has spacious rear seats. It's a shame, then, that the boot is on the small side.

Read our full Ford Focus review

Reliability
Safety
Costs
Quality
Performance

Strengths

  • Class-leading interior quality
  • Smooth engines
  • Well-equipped

Weaknesses

  • Entry-level engines are a touch weedy
  • A BMW 3 Series is more fun to drive
  • You can’t add many options

Real MPG Average 52.2mpg | Town 45.6mpg | Motorway 46.2mpg | Rural 67.0mpg

Not only does the Audi A4 35 TDI have the most economical engine in the A4 range, but it's also our overall pick of the bunch. It has more than enough grunt to whisk you to motorway speeds effortlessly (0-62mph takes 8.2sec), and it's smoother and quieter than the equivalent diesel engine in its Mercedes C-Class rival. The A4 also has the best-built interior in its class, and it beats the BMW 3 Series when it comes to ride comfort.

Read our full Audi A4 review

Our pick: 420i M Sport 2dr Step Auto

0-62mph: 7.5 sec
MPG/range: 44.8mpg
CO2 emissions: 144g/km
Seats: 4
Boot: 440 litres
Insurance group: 29E

Strengths

  • Smart styling
  • Involving to drive
  • High-quality interior

Weaknesses

  • Noisy four-cylinder diesel engines
  • Firm ride on bigger wheels
  • Touch of wind noise at speed

Real MPG Average 52.0mpg | Town 46.4mpg | Motorway 45.2mpg | Rural 67.7mpg

It has since been replaced by an all-new model, but the previous BMW 4 Series Coupé is still an elegant and efficient choice. Although there were more powerful engine options, this 2.0-litre 420d model strikes the best balance between performance and costs. The 4 Series is well equipped and fun to drive, plus there's space for four inside. It's also available as a convertible if you're looking for roof-down thrills.

Read our full used used BMW 4 Series (2013-2020) review

And the least economical hybrid cars...

Ssangyong Musso 2.2

Real MPG Average 29.0mpg | Town 20.5mpg | Motorway 28.7mpg | Rural 37.2mpg The Ssangyong Musso is the only pick-up on our list, so in isolation it seems harsh to criticise it. But the Ford Ranger, Isuzu D-Mac and Toyota Hilux all return between six and 7.5mpg m... Read our review

Audi Q7 50 TDI

Real MPG Average 27.2mpg | Town 22.5mpg | Motorway 24.6mpg | Rural 35.0mpg The Audi Q7 has many great attributes: it's brilliantly built, smooth to drive and the engines are punchy. And in the case of the 50 TDI, fast, too. But it's also thirsty. Rural economy... Read our review

Land Rover Discovery 3.0 HSE Luxury

Real MPG Average 26.3mpg | Town 20.3mpg | Motorway 25.3mpg | Rural 32.6mpg You might expect a heavy SUV with a big engine to offer paltry economy, but the Discovery is at the foot of our list. It doesn't impress in any particular area of economy. Since we teste... Read our review