Most economical cars

The best mpg cars with the lowest CO2 emissions: these are the most economical cars - with petrol or diesel engines - available now

BuyaCar team
Aug 13, 2018

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

The most frugal option is a hybrid car - particularly if it's a plug-in hybrid with a battery that can be charged up for miles of emissions-free motoring. 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 a government grant if you buy them new. In London, they are all exempt from the congestion charge.

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 of brand new models. It's not uncommon for mpg ratings of used cars to be slightly different.

The official mpg figures quoted are only a guideline: fuel economy of plug-in hybrid cars varies wildly depending on how they are used. They are particularly efficient on short journeys of under 30 miles, where they mainly run on battery power (if fully recharged). On longer trips, where they are largely powered by an engine, fuel economy is closer to a conventional car and so their higher cost may not result in worthwhile savings.

Most economical cars 2018


1. Toyota Prius Plug-in 1.8 VVT-I auto

Best economical car for efficiency on all journeys

CO2 22g/km  Official fuel economy 283mpg
Latest Toyota Prius Plug-in deals (current model) from £21,999
Finance from £297 per month

The Prius Plug-in's official mpg figure is a stratospheric 283mpg 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. The minimal 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. The current-generation car was launched in 2017, so remains fairly expensive. Older models cost from £14,990 but have much less electric range - around 12 miles on one charge.


2. Hyundai Ioniq PHEV

Best economical car for an affordable price

CO2 26g/km Official fuel economy 256.8mpg
Latest Hyundai Ioniq PHEV deals from £19,337
Finance from £265 per month

The large battery packs in plug-in hybrid cars usually makes them several thousands of pounds more expensive than standard models but you can pick up a nearly-new Ioniq PHEV from £19,337 and a new model for less than £26,000, which brings it into line with some diesel cars. It's certainly more efficient than them, even if the official fuel economy figure doesn't really reflect what you can expect.

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 the 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. Hyundai also makes a non-plug-in version of the Ioniq, which is less efficient but cheaper, with prices starting from £200 or £200 per month.


3. Kia Niro PHEV

Best economical car for efficiency with a long warranty

CO2 29g/km  Official fuel economy 217.3mpg

With hybrid power and a high driving position, the Kia Niro should be the perfect car for modern roads, offering excellent fuel economy and a crossover design, which should offer the visibility and practical benefits of an off-road car, with the comfort and stability of a standard hatchback. It’s one of the more affordable plug-in hybrid cars too, with new prices starting at well below £30,000, when the government’s grant is taken into account.

The hybrid system will power the car on electric energy along for around 25 miles. It does reduce boot space to 324 litres - less than you’ll find in a VW Polo, but the passenger area is spacious enough to carry adults in the front and back. For more boot space, but reduced fuel economy, a non-plug-in hybrid Niro is available, costing from £18,673 or £242 per month.

Like all Kias, the Niro has a seven-year warranty - limited to the first 100,000 miles - providing plenty of reassurance that it will last.
Kia Niro buying guide


4. Kia Optima PHEV 2.0 GDi

Best economical car for efficiency with a long warranty

CO2 33g/km Official fuel economy 201.8mpg
Latest Kia Optima PHEV deals from £19,501
Finance from £286 per month

The Kia Optima doesn’t just have a range of around 30 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 most efficient version is the Sportswagon estate, but there's also an Optima saloon with a smaller boot and reduced electric range.

The Optima PHEV benefits from Kia’s seven-year / 100,000 mile warranty but not the manufacturer’s traditionally cheap prices from new. However, used prices have dropped to below £20,000, which is equivalent to a Mitsubishi Outlander PHEV and only slightly cheaper than a BMW 330e. Both cars are subject to the same rate of company car tax.
Kia Optima Sportswagon buying guide


5. Audi A3 Sportback e-tron

Best economical car for Audi quality & low company car tax

CO2 38g/km Official fuel economy 166.2mpg
Latest Audi A3 e-tron deals from £16,499
Finance from £204 per month

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, and you can expect around 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. The figures are identical to the VW Golf GTE below, as both cars share the same mechanical parts.
Audi A3 buying guide


6. Volkswagen Golf

Best economical car for brisk performance

CO2 38mpg  Official fuel economy 166.2mpg
Latest VW Golf GTE deals from £7,999
Finance from £135 per month

It’s no accident that this car sounds a bit like Volkswagen’s famous sporty Golf GTI. When the Golf GTE’s electric motor and its petrol engine combine to power the car at the same time, the car can really shift, accelerating from 0-62mph in 7.6 seconds. The weight of this plug-in hybrid car’s batteries means that it’s not as nimble in corners as the GTI, though.

As with other plug-in hybrids, the Golf GTE is expensive but brings considerable company car tax benefits. Running costs will be low if you travel less than 25 miles between charging up, when the car should run without the petrol engine for most of the time. It's so popular that there are lengthy delays for brand new models but plenty of used and nearly-new cars are available.
VW Golf GTE buying guide


7. Volkswagen Passat GTE

Best economical car for business users who need a big boot

CO2 40g/km Official fuel economy 156.9mpg
Latest VW Passat GTE deals from £27,000
Finance from £383 per month

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 £27,000, which makes it competitive.
VW Passat buying guide


8. Audi Q7 e-tron

Best economical car for the highest fuel economy from an SUV

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 run on 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 eligible 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.
Audi Q7 buying guide


9. BMW 330e

Best economical car for green performance

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, which has made the BMW 330e a hit for the company. There's a large amount of choice on the used market with 33 cars currently available on BuyaCar.

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 standard BMW 3 Series but long distance fuel economy of around 50mpg (based on gentle driving) is impressive for a petrol car.
BMW 3 Series buying guide


 10. Mitsubishi Outlander PHEV

Best economical car for SUV practicality without the price premium

CO2 44g/km Official fuel economy 148.5mpg
Latest Mitsubishi Outlander PHEV deals from £13,495
Finance from £200 per month

Excluding the all-electric Tesla Model X, the Mitsubishi Outlander PHEV has the lowest CO2 emissions of any sport utility vehicle (SUV) on the market, with an official figure of 44g/km - even though the Audi Q7 e-tron has a better mpg figure.

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.
Mitsubishi Outlander PHEV buying guide


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