Most economical cars: best mpg cars of 2019

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

BuyaCar team
Mar 19, 2019

If you want the very greenest car on the road, then you’ll need an electric car. But if you want to be eco-friendly and have the reassurance of a conventional engine, then the most economical cars available to you are plug-in hybrids.

These have 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. In London, they are all exempt from the congestion charge.

If you can keep the car charged regularly, then the fuel savings should roll in. However, they aren't for everyone. They are comparatively expensive to buy and less effective on long trips, where battery power is rarely used and fuel economy can be worse than a standard petrol or diesel model.

There are plenty of economical and cheaper alternatives to plug-in hybrids, and you can find more information in the guides listed below.

Alternatively, scroll down for the most economical cars, based on official mpg figures. We've used figures from the latest test method, known as WLTP, which is more accurate than earlier procedures. They still don't fully reflect real-world driving, though, and that's particularly the case when it comes to plug-in hybrids. Wheel sizes and equipment levels can also affect fuel economy.

Because they use no fuel when running on electric power, but rely mainly on an engine during longer journeys, the fuel economy of plug-in hybrids will vary wildly, depending on how they are used and if the battery is charged.


Most economical cars 2019


1. Hyundai Ioniq PHEV

Best economical car for efficiency on all journeys

Latest Hyundai Ioniq PHEV deals from £20,500
Finance from £303 per month 
Hyundai Ioniq PHEV 247.8mpg / 26g/km CO2

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 £20,500 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, the car remains frugal, with motorway fuel economy of 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 £216 or £216 per month.


2. Toyota Prius Plug-in

Best economical car for futuristic design

Latest Toyota Prius Plug-in deals from £21,594
Finance from £273 per month 
Toyota Prius Plug-in 235mpg / 28g/km CO2

The Prius Plug-in's official mpg figure is a stratospheric 235mpg 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 - much like the Ioniq, above - 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 £21,594 but have much less electric range - around 12 miles on one charge.


3. Kia Niro PHEV

Best economical car for a high driving position

Kia Niro PHEV 201.8mpg / 31g/km CO2

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 just over £30,000 and used models available for less.

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 £16,495 or £229 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. Mercedes E-Class

Best economical car for diesel and petrol options

Latest Mercedes E-Class diesel deals from £13,499
Finance from £212 per month  
Mercedes E 300 de 201.8 / 41g/km CO2

If you're looking for an efficient Mercedes E-Class, then you have the choice of a petrol or diesel plug-in hybrid car. Both the Mercedes E 300de (diesel) and E 300e (petrol, pictured) have official fuel economy figures of more than 150mpg and carbon dioxide emissions that put them into the lowest company car tax bracket, although the diesel version is subject to a 4% surcharge.

This makes the petrol car the best choice for anyone looking for the lowest company car tax and the diesel version the pick for buyers who are looking for the best fuel economy in all situations: an electric range of around 30 miles in real-world conditions (take off around two miles if you choose the estate car) is ideal for short commutes, while the efficiency of the diesel engine will cut costs on longer journeys.
Mercedes E-Class buying guide


5. Kia Optima PHEV 2.0 GDi

Best economical car for efficiency with a long warranty

Kia Optima PHEV
188.3 / 34g/km CO2

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 of a similar age 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


6. Mitsubishi Outlander PHEV

Best economical car for SUV practicality without the price premium

Latest Mitsubishi Outlander PHEV deals from £13,299
Finance from £206 per month
Mitsubishi Outlander PHEV
139.7mpg / 40g/km CO2

This five-seat, four-wheel drive off-roader has been exceptionally popular with buyers looking to pay the lowest level of company car tax because of low CO2 emissions and a grant from the government that reduced the price. It’s 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.

Recent updates have kept the design of the Outlander looking fresh, but the car is being caught up by more modern competitors, such as the Kia Niro PHEV, above, with a more comfortable ride and better-quality interiors. The price advantage is also reducing too, now that the government has removed the grant for plug-in hybrid vehicles. All-electric models, such as Kia's eNiro and the Hyundai Kona Electric have a similar price, and will also benefit from much lower company car tax next year.
Mitsubishi Outlander PHEV buying guide


7. BMW 5 Series

Best economical car for dapper looks and driving fun

Latest BMW 530e deals from £25,995
Finance from £326 per month 
BMW 530e
128.4mpg / 49g/km CO2

BMW's plug-in hybrid 5 Series just squeezes in to the lowest company car tax bracket (until next year), bringing improved fuel economy without dramatically affecting the sporty driving experience that makes the car popular with buyers.

A fully-charged battery will take the car around 20 miles in normal driving, with barely any assistance from the petrol engine, but the car's automatic mode is best for fuel economy on longer trips, as it switches between engine and motor for the most efficient performance.

Performance is the right word, as the car accelerates from 0-62mph in a swift 6.2 seconds and retains its agility when changing direction, which makes it fun to drive. You will have to put up with a slightly bumpier ride on rough surfaces - due to the extra battery weight - and a smaller boot, which offers roughly as much space as a Volkswagen Golf.
BMW 5 Series buying guide


8. BMW i8

Best economical car for speed

Latest BMW i8 deals from £49,000
Finance from £590 per month 
BMW i8
128.4mpg / 42g/km CO2

The BMW i8 first appeared five years ago, but it still turns heads, as the embodiment of BMW's belief that electric and hybrid cars can remain exciting to drive. Of course, if you do drive it in the enthusiastic manner intended, then fuel economy is not going to be particularly impressive: the electric motor and petrol engine are best-suited to working together, delivering instant acceleration that continues to the legal limit and beyond.

Even so, switch it to eDrive mode and you can drive the i8 for around 30 miles on electric power alone. This makes it more efficient than a typical supercar. Restrained use of the accelerator on longer trips should result in fuel economy that matches a Ford Focus, but don't expect the 100mpg-plus figures that the official tests record.
BMW i8 buying guide


9. Mercedes S-Class

Best economical car for the 1%

Mercedes S 560e
128.4mpg / 57g/km CO2

There's no surprise that the company car tax advantages of this plug-in version of the Mercedes S-Class are what makes it particularly attractive: Additional Rate 45% taxpayers will save almost £4,500 per year compared with a standard diesel model.

But the luxury car is also likely to do its bit to reduce urban emissions, as it transports executives from one city meeting to another in sumptuous surroundings: the electric range of around 30 miles with a full battery may be enough for a whole day's schedule. A home charger will take around three hours for a full recharge.

Efficiency drops off considerably once the battery is exhausted and the large petrol engine takes over; the diesel model is better for long motorway journeys. The car does its best, though. When you - or more likely your driver - are behind the wheel,. you'll see prompts to lift off the accelerator at just the right moment, to allow you to coast to a junction or a slower speed limit, avoiding the need to brake hard and waste energy.


10. Volvo S90 / V90

Best economical car for Scandi-chic

Volvo S90/V90 T8
117.7mpg / 49g/km CO2

Volvo estate cars are no longer the biggest in the business. For a brand that made its name with cavernous square-shaped load carriers, that could have come as an embarrassment if it hadn't focused on standing out in a totally different area: style.

For while the BMW 5 Series Touring, Mercedes E-Class Estate and Skoda Superb Estate all offer more luggage space, it's not particularly controversial to suggest that the V90 is much better looking. That goes for the interior too, where a large touchscreen controls virtually every function, leaving calm minimalism across the rest of the dashboard. It no longer looks as cutting edge as it did when the car was first launched, but still creates a calming effect as soon as you open the door.

You can expect around 20 miles of range on electric power alone from the hybrid T8 model - 10 miles short of the official figure. Longer distances will see fuel economy tumble, as the petrol engine hauls the two-ton car on its own. Given the car's price of almost £60,000 when new, before discounts, and the limited availability of used models, it's only likely to appeal to company car users who will feel the benefit of the 49g/km CO2 emissions that bring the lowest rate of company car tax. And despite being overtaken by some rivals, the V90's boot is still pretty enormous.
Volvo V90 buying guide


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