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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
Stuart Milne
Updated: 20 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.
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 >>
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Skoda Octavia
Best buy: 1.5 TSI e-TEC MHEV ACT SE L DSG Euro 6 (s/s) 5dr
0-62 mph: 8.5 sec
MPG/range: 57.6 mpg
C02 emissions: 112 g/km
Seats: 5
Boot: 600 litres
Insurance group: 20E
Driving
Interior
Practicality
Buying & Owning
Strengths
- Spacious 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
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Best price from £28,740
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The What Car? best price shows you the cheapest way to buy your new car, whether it's by choosing an in-stock car through our partner Autotrader or placing a factory order.
Available now from: £29,790
RRP from: £28,740
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From £23,495
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From £303
About our price indicator
What Car? indicative Personal lease example (subject to status)
Skoda Octavia
Expected annual mileage 5000 Term months 24 Deposit months 12 Monthly payment £302.68 Initial payment £3,632.16
Step-by-step
Leasing works a bit like a long-term rental. You drive it, but you don’t own it.
- Choose your car, pick your terms and apply for lease credit online
- Pay monthly rental payments for your chosen term length
- Drive it, enjoy it, then give it back at the end
What you get
When you lease with Autotrader you get all of this:
- Full manufacturer’s warranty
- Road tax and roadside assistance included
- Free returns within 30 days*
Excess mileage charges and return conditions apply. Subject to availability and credit status. 18+ T&Cs apply.
In partnership with
£3,877 total upfront (£3,632 initial rental plus £245 processing fee) | 5000 miles | 24 months
- Lower total monthly cost than PCP/HP
- No balloon payments
- Road tax included
Used Vauxhall Astra 2015-2021
Strengths
- Spacious interior
- Relatively cheap to buy
- Well equipped
Weaknesses
- Vague steering
- Diesels can be noisy
- Low-speed ride can be fidgety
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
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Used Seat Leon 2013-2020
Our pick: 1.5 eTSI MHEV SE Dynamic DSG Euro 6 (s/s) 5dr
0-62 mph: 10.4 sec
MPG/range: 53.3 mpg
C02 emissions: 121 g/km
Seats: 5
Boot: 380 litres
Insurance group: 14E
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
Used car deals
Used Renault Kadjar 2015-2022
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
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Skoda Superb Estate
Best buy: 1.5 TSI e-TEC MHEV SE Technology DSG Euro 6 (s/s) 5dr
0-62 mph: 9.3 sec
MPG/range: 56.5 mpg
C02 emissions: 118 g/km
Seats: 5
Boot: 690 litres
Insurance group: 23E
Driving
Interior
Practicality
Buying & Owning
Strengths
- Hugely spacious boot and interior
- Comfortable on adaptive (DCC) suspension
- Well equipped and priced – PHEV makes a cheap company car
Weaknesses
- Grabby brakes on the PHEV
- Interior quality not the best in places
- 3 Series Touring is 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
New car deals
Best price from £38,060
What is What Car? best price?
The What Car? best price shows you the cheapest way to buy your new car, whether it's by choosing an in-stock car through our partner Autotrader or placing a factory order.
Available now from: £38,060
RRP from: £38,430
Nearly new deals
From £26,495
Leasing deals
From £274
About our price indicator
What Car? indicative Personal lease example (subject to status)
Skoda Superb Estate
Expected annual mileage 5000 Term months 24 Deposit months 12 Monthly payment £273.78 Initial payment £3,285.36
Step-by-step
Leasing works a bit like a long-term rental. You drive it, but you don’t own it.
- Choose your car, pick your terms and apply for lease credit online
- Pay monthly rental payments for your chosen term length
- Drive it, enjoy it, then give it back at the end
What you get
When you lease with Autotrader you get all of this:
- Full manufacturer’s warranty
- Road tax and roadside assistance included
- Free returns within 30 days*
Excess mileage charges and return conditions apply. Subject to availability and credit status. 18+ T&Cs apply.
In partnership with
£3,530 total upfront (£3,285 initial rental plus £245 processing fee) | 5000 miles | 24 months
- Lower total monthly cost than PCP/HP
- No balloon payments
- Road tax included
Used Ford Mondeo Hatchback 2014-2022
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
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Used Vauxhall Insignia Grand Sport 2017-2022
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
Used car deals
Ford Focus
Reliability
Safety
Costs
Quality
Performance
Strengths
- Great handling
- Well equipped
- Roomy rear seats
Weaknesses
- Grey, cheap-feeling interior
- Seat Leon is more affordable
- Skoda 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
New car deals
Best price from £26,275
What is What Car? best price?
The What Car? best price shows you the cheapest way to buy your new car, whether it's by choosing an in-stock car through our partner Autotrader or placing a factory order.
Available now from: £26,275
RRP from: £29,575
Nearly new deals
From £18,290
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Audi A4
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
New car deals
Best price from £32,725
What is What Car? best price?
The What Car? best price shows you the cheapest way to buy your new car, whether it's by choosing an in-stock car through our partner Autotrader or placing a factory order.
RRP from: £32,725
Nearly new deals
From £895
Used BMW 4 Series Coupé 2013-2020
Strengths
- Smart styling, especially in the higher trims
- Involving to drive, with eager steering and agile handling
- High-quality interior, with premium materials
Weaknesses
- Noisy four-cylinder diesel engines
- Firm ride on bigger wheels, especially on M Sport
- Touch of wind noise at speed from around mirrors
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
Used car deals
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 more.
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 is reasonable for such a large SUV, but elsewhere fuel economy is poor.
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 tested the car, a mild-hybrid version has been introduced which should help to reduce those fuel bills.
Read our review
Real MPG
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