Most economical cars

The best mpg cars with the lowest CO2 emissions: the most economical cars - with petrol or diesel engines - that you can buy

BuyaCar team
Nov 1, 2017
Lakov Kalinin / Shutterstock

If you want the very greenest car on the road, then you’ll need an electric car - or one of the very few powered by hydrogen. But if you can’t charge your car at home, or don’t want the hassle of doing so on long journeys, then there are plenty of alternatives that offer eco-friendly motoring.

Thee are plenty of efficient petrol and diesel cars available and the most frugal are hybrid cars - particularly plug-in hybrids that can be charged up like an electric car to give emissions-free motoring for several miles. When power runs low, a petrol or diesel engine takes over so you don't have to stop and recharge. With carbon dioxide (CO2) emissions of less than 50g/km, these cars are in the very lowest company car tax bands and many benefit from government grants of £2,500 if you buy them new. In London, they are all exempt from the congestion charge.

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Below are the most efficient petrol or diesel cars that you can buy. They aren't necessarily the best cars on sale (see the best used tax exempt cars) but are rated as the most economical, based on official mpg figures. Their low CO2 emissions also means good fuel economy, so these are among the best mpg cars available.

These figures are only an indication of the car’s fuel economy: the mpg of plug-in hybrid cars varies wildly depending on how they are used. On short journeys of under 30 miles, they use little or no fuel because they can run purely on battery power. In these circumstances, they can save you a lot of money. But on longer trips, where they are mainly powered by their engine, fuel economy will be closer to a conventional car and so their higher cost may not result in worthwhile savings.

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Most economical car 2017

Toyota Prius Plug-in 1.8 VVT-I auto

Best economical car to choose for efficiency on all journeys
Prices from £25,000
CO2 22g/km  Official fuel economy 282.5mpg

The Prius Plug-in's official mpg figure is a stratospheric 282.5mpg but you can even improve on that if your commute is less than 30 miles long, because the car will cover virtually all of that distance on electric power alone. Even when the petrol engine starts up, fuel economy is still pretty good - gentle driving can return 70mpg on a long motorway drive. The price for this is fairly sedate performance.

If you live and mainly drive in the city, then the chances are that you'll rarely need to visit a petrol station, but the Prius' all-round efficiency should result in low-cost motoring, however it's used. It only went on sale this year, so there are a limited number of second-hand models available. Its low 22g/km CO2 figure is outstanding but given that the lowest band of company car tax is 1-50g/km CO2, it won't earn you any additional tax saving.

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Second most economical car 2017

Hyundai Ioniq PHEV

Best economical car to choose for an affordable price
Prices from £20,000 (used)
CO2 26g/km Official fuel economy 256.8mpg

The large battery packs in plug-in hybrid cars usually makes them several thousands of pounds more expensive than standard models - even when government discounts are taken into account. But you can pick up a nearly-new ioniq for just under £20,000 and a nw model for less than £24,000, which brings it into line with some diesel cars. It's certainly more efficient than them, even if the official fuel economy figure of almost 257mpg doesn't really reflect what you can expect from the Ioniq.

When fully charged, the Ioniq has a range of 25 to 30 miles on electric power alone, although the petrol engine does power up to provide a boost when you push the accelerator hard. Beyond battery power, you can expect motorway fuel economy similar to ther Prius Plug-in, with more than 70mpg possible if you drive smoothly. That's not difficult as the engine lacks the power for speedy acceleration.

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Third most economical car 2017

Kia Optima PHEV 2.0 GDi

Best economical car to choose for efficiency with a long warranty
Prices from £19,000 (used)
CO2 37g/km Official fuel economy 176.6mpg

The Kia Optima doesn’t just have a range of 33 miles on electric power alone, but an efficient petrol engine too, so fuel economy remains good even when the battery is low and the engine fires up. You do feel that the car has been engineered for efficiency - unfortunately in its slow acceleration.

The Optima PHEV benefits from Kia’s seven-year / 100,000 mile warranty but not the manufacturer’s traditionally cheap prices from new. However, there are now 2016 cars available for under £20,000, saving almost £10,000 on the new Kia Optima price - which is equivalent to a Mitsubishi Outlander PHEV and only slightly cheaper than a BMW 330e, which is subject to the same rate of company car tax.

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Fourth most economical car 2017

Audi A3 Sportback e-tron

Best economical car to choose for Audi quality at low company car tax rates
Prices from £20,000 (used)
CO2 38g/km Official fuel economy 166.2mpg

A plug-in hybrid version of Audi’s highly popular A3 Sportback family car, the e-tron offers low emission motoring, with the same style and quality feel of any other Audi. Its electric motor can power the car at speeds of up to 81mph for up to 29 miles, although you’ll be lucky to get more than 20 miles of range.

The motor will also combine with the petrol engine to provide zippy performance, Official figures state that the car has CO2 emissions of 38g/km, so it qualifies for the lowest rate of company car tax.
Read the Audi A3 buying guide

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Fifth most economical car 2017

Volkswagen Passat 1.4 TSI GTE

Best economical car to choose for Business users who need a big boot
Prices from £25,000 (used)
CO2 40g/km Official fuel economy 156.9mpg

The VW Passat GTE plug-in hybrid offers similar performance to the Golf GTE, but with more space because it's available as a saloon or estate car. With official CO2 emissions of 39g/km, it's in the lowest band for company car tax, although the powerful petrol engine (compared with those in the Prius and Ioniq) means that fuel economy does fall when the fully-charged battery range of around 25 miles is up.

You can expect around 50-60mpg on long journeys, but acceleration is considerably more rapid than in the Toyota or Hyundai. The hefty list price of £37,000 might dent the appeal of the car, but there are new car discounts of more than £11,000 and used models starting from £25,000, which makes it competitive.

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Sixth most economical car 2017

Audi Q7 e-tron

Best economical car to choose for the greenest large SUV
Prices from £50,000 (used)
CO2 48g/km Official fuel economy 156.9mpg

From gas guzzler to green giant: Audi’s Q7 looks like the last word in conspicuous consumption but the e-tron version contains a big battery. That allows the heavy SUV to roll along, powered by electricity for up to 34 miles - although that range will quickly reduce at higher speeds.

It’s efficient - bearing in mind its size - on longer trips too, thanks to the diesel engine under the bonnet. Just don’t expect to see a windfall from lower fuel prices, as you pay a big premium of more than £10,000 when new over the standard Q7 and it's not eleigible for a government grant. Used prices from £50,000 are slightly more affordable.

The extra space required by the car's battery pack means that it’s only available with five seats rather than the seven available with other versions.
Read the Audi Q7 buying guide

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Seventh most economical car 2017

Volvo V60 2.4 D5 Twin Engine Hybrid

Best economical car to choose for families who want a diesel plug-in hybrid
Prices from £21,000 (used)
CO2 48g/km Official fuel economy 155.2mpg

It’s got low emissions of 48g/km CO2 - according to official figures - but the V60 D5 Twin Engine looks to be an expensive option, with a list price of more than £38,000.

So it’s no surprise that you can get more than £6,000 off the cost of a new car (including government grant), and a used model for almost half price. It buys you a plug-in hybrid estate car that can go up to 32 miles on battery power and, unusually for a car this size, has a diesel engine too, which helps keep the car relatively efficient on longer journeys. It’s in the lowest company car tax bracket but business users shouldn't expect rock-bottom rates because the tax that they pay is also based on the car's high list price.

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Eighth most economical car 2017

BMW 330e iPerformance

Best economical car to choose for green performance
Prices from £22,000 (used)
CO2 44g/km Official fuel economy 148.7mpg

It’s one of the most popular company cars and this version qualifies for the lowest rate of company car tax. That’s the reason that the plug-in hybrid BMW 330e iPerformance exists: the official emissions figure of 44g/km CO2 means that it sits in the lowest tax bracket.

It’s got a range of around 20 miles on battery power alone, but - just as relevant - the 330e also has impressive performance, when the electric motor and petrol engine combine to provide maximum power. It might not be as agile or quite as comfortable as the standrd car but long distance fuel economy of around 50mpg (based on gentle driving) is impressive for a petrol car.
See the BMW 3 Series buying guide

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 Ninth most economical car 2017

Mitsubishi Outlander PHEV

Best economical car to choose for SUV practicality without the price premium.
Prices from £14,000 (used)
CO2 44g/km Official fuel economy 148.5mpg

Excluding the all-electric Tesla Model X, the Mitsubishi Outlander PHEV has the lowest CO2 emissions of any SUV on the market, with an official figure of 44g/km.

This five-seat, four-wheel drive off-roader has been exceptionally popular with buyers looking to pay the lowest level of company car tax. It’s also good for economical short journeys, with the ability to drive for up to 32 miles in all-electric mode. But it’s much less efficient on long journeys, when the petrol engine has to work hard to keep the heavy SUV moving.

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Tenth most economical car 2017

BMW 225xe Active Tourer

Best economical car to choose for the space of a people carrier with the lowest emissions in its class
Prices from £27,000 (used)
CO2 46g/km Official fuel economy 141.2mpg

The 2 Series Active Tourer is the people carrier for families who can’t face driving a minibus - and can afford the BMW prices.

They’ll have to dig even deeper for the greenest version, which costs more than £30,000, but this does buy the most efficient petrol people carrier on the market, with official CO2 emissions of 46g/km and 141mpg. The ability to go for up to 24 miles on electric power alone will make school runs silent and squeaky clean.

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