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What’s the most fuel-efficient type of car?

Our handy guide to how petrol and diesel cars compare with hybrids and electric cars when it comes to efficiency

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One day in the not too distant future, we’ll all be driving around happily in our electric cars.

But until then, today’s purchase requires a big decision – petrol, diesel, hybrid or electric.

To help you make this decision, we help you understand the best options in each category.

Hybrid sales are on the rise, thanks to the greater availability of models, but also because official figures for fuel consumption and CO2 emissions are very impressive.

Why are there the three choices?

Carmakers have spent billions to address climate change, making their cars more fuel efficient and less polluting.

As governments introduced laws to reduce carbon dioxide, manufacturers concentrated on diesel, as these cars emit less CO2 than petrol.

They can also go further on a litre of fuel than petrol cars.

However, now that air quality has become a bigger issue, other emissions (particularly nitrogen oxides, or NOx) mean that diesel is less popular.

Diesel cars are still more efficient than petrol ones, and the emissions from the latest diesel engines have been reduced significantly, so they’re still worth considering for high-mileage drivers. 

Petrol cars are typically slightly cheaper than diesel ones, and are also typically taxed at a higher rate and don’t come with things like diesel particulate filters (DPF), which require extra maintenance. 

Electric cars for efficiency

Electric cars, or electric vehicles (EVs), and hybrids that use electric motors alongside conventional engines are becoming more popular.

EVs emit no CO2 or other emissions when running.

Hybrids use a conventional engine, but also have electric motors, so their fuel consumption and CO2 emissions are better than petrol or diesel cars.

With so many choices, what’s best for you?

Most economical petrol cars

The fuel efficiency of petrol cars has improved in recent decades.

Smaller turbocharged engines produce more power, so many petrol cars can deliver more than 50mpg.

Logically, small cars are the most efficient.

So, look at city cars such as the Volkswagen up!, Suzuki Celerio, Seat Mii, Škoda Citigo and Kia Picanto to reduce your fuel bills, while the Seat Ibiza, Suzuki Baleno and Dacia Sandero also offer real-world figures in excess of 50mpg, but are slightly larger superminis.

Most economical diesel cars

The popularity of diesel cars has taken a dive in recent years, because of their ‘dirty’ NOx emissions.

However, the diesel engines in new cars mean that emissions are now cleaner than they were.

And because diesel engines use 15−20% less fuel that petrol cars, running costs are lower.

Again, small is better, so look to the Peugeot 208 1.5 BlueHDi 100, Ford Focus 1.5 EcoBlue 95PS, Honda Civic 1.6 i-DTEC and the Renault Megane dCi 115, while the Mercedes-Benz C 200 d executive saloon can also exceed 60mpg.

Best hybrid cars

Hybrid sales are on the rise, thanks to the greater availability of models, but also because official figures for fuel consumption and CO2 emissions are very impressive. And because CO2 figures are low, car tax is low.

Hybrids have an electric motor alongside a petrol or diesel engine, and the car’s electronic systems switch between the two to maximise efficiency.

So, for example, in stop-start urban traffic, the electric motor works best, while on a free-flowing motorway, the conventional engine is better.

The different types of hybrids

There are several types of hybrid, so it’s important to know the differences between them if you’re intending to buy a hybrid.

The hybrids most people think of are what’s known as parallel or self-charging hybrids.

These are powered either directly by the engine, or by the electric motor alone, or by both working together.

The battery gets charged when you slow down or brake, from a regenerative braking system. 

Toyota and Lexus cars mostly use this technology. The Hyundai Ioniq hatchback and Ford Mondeo Hybrid are others.

The plug-in hybrid (PHEV) uses the same braking system to charge the batteries for the electric motor, but the car can also be plugged in to charge.

These have a longer electric-only range of around 20-30 miles, when they don’t need the petrol of diesel engine.

There are now lots of PHEV models on sale, including the Audi A3 e-tron, Volkswagen Golf GTE, Mini Countryman, Mitsubishi Outlander, BMW 330e and the Mercedes-Benz E 300 de diesel hybrid. There’s even a BMW i8 plug-in sports car.

Mild hybrid cars for efficiency

Finally, there are mild (or 48V) hybrid cars, where the motor just gives a little boost to the engine, not actually power the car.

You’ll find this system in cars such as the Suzuki Swift, Kia Sportage, Hyundai Tucson, and versions of the Audi A6, A7 and A8.

Best electric cars

Figures from the Energy Savings Trust suggest that running an electric car costs around £2-4 for about 100 miles, while a petrol or diesel car will cost around £13-15 per 100 miles.  

The EVs worth considering are the BMW i3, Nissan Leaf and Renault Zoe, but their ranges aren’t huge.

Cars with longer ranges (250+ miles) include the Hyundai Kona, Kia e-Niro, Jaguar I-Pace and Audi e-tron.

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