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A fuel-efficient car could save you up to £836 a year

Choosing the right car will save you a boat load of cash at the fuel pump

£836 – every year. That’s how much you’ll save on fuel by buying the most efficient medium-sized car we’ve tested compared to the worst – the VW Beetle.

Along with long-range weather forecasts and psychic predictions, official mpg figures shouldn’t be taken at face value. Over the years Which? car testing has proven the fuel economy you get from your car in real life is almost never as good as the official mpg from the car’s glossy brochure.

Our in-depth car reviews publish a realistic fuel economy for every car, directly from our tests. But that’s only half the story. Our annual car survey reveals big differences in annual mileage depending on the type of car you drive – and that adds up at the fuel pump. Think 10,000 miles is average? Think again.

The Which? Car Survey lets us identify which are the most and least reliable cars and much more. This year’s survey is open until 1 March.

What you’ll really pay for fuel

A recent Which? study found that the cost of fuel is currently a key consumer concern, and to make matters worse, fuel prices are rising.

If you’re considering buying a car, it’s more important than ever that you know how much it’s going to cost you to run. That means knowing both the car’s true fuel economy, and how far you’re likely to travel in it.

According to our survey, drivers of small and city cars drive 7,245 miles a year on average, while for medium cars it’s 9,147 and for large cars it’s 10,361.

Below you’ll find the most and least efficient fuel economies we’ve found so far, for cars currently on sale as new. We’ve named the biggest fuel users, but to reveal the identity of the most fuel-frugal car, head for our guide to the most fuel-efficient cars.

City cars

Owners of these dinky little runabouts have, unsurprisingly, one of the lowest annual mileages in our survey.

Most efficient city car

Tested economy: 56.5mpg

Claimed fuel economy: 68.9mpg

Engine: 1.0-litre petrol, 69hp

Annual fuel cost: £637

Visit our guide to the most fuel-efficient city cars to see which model we’re talking about.

Least efficient city car: Vauxhall Adam Rocks

Tested economy: 41.5mpg

Claimed fuel economy: 47.9mpg

Engine: 1.4-litre petrol, 150hp

Annual fuel cost: £867

Difference between the most and least efficient city car: £230 a year.

Small cars

Small cars are big business. The Ford Fiesta is in this segment – it’s the highest-selling car in the UK according to figures published by the Society of Motor Manufacturers & Traders (SMMT). This class also includes big hitters like the VW Polo and Mazda 2.

Most efficient small car

Tested economy: 74.3mpg

Claimed fuel economy: 83.1mpg

Engine: 1.5-litre diesel, 105hp

Annual fuel cost: £486

Visit our guide to the most fuel-efficient small cars to find out which model we’re talking about.

Least efficient small car: Renault Clio

Tested economy: 42.2mpg

Claimed fuel economy: 44.8mpg

Engine: 1.6-litre petrol, 200hp

Annual fuel cost: £852

Difference between the most and least efficient small car: £366 a year.

Medium cars

Medium-sized cars house some fiercely popular cars like the VW Golf, Ford Focus and Vauxhall Astra. They have to be practical and often function as family cars, but our tests below reveal a whopping £800 gap between the least and most fuel-efficient car in this class.

Most efficient medium car

Tested economy: 85.6mpg

Claimed fuel economy: 166.2mpg

Engine: 1.4-litre petrol-hybrid, 200hp

Annual fuel cost: £530

Visit our guide to the most fuel-efficient medium cars to see which model we’re talking about.

Least-efficient medium car: Volkswagen Beetle

Tested economy: 34mpg

Claimed fuel economy: 36.7mpg

Engine: 2.0-litre petrol, 200hp

Annual fuel cost: £1,336

Difference between the most and least efficient medium car: £836 a year.

Large cars

Owners of large cars like the Ford Mondeo, Audi A5 and Hyundai i40 cover the highest number of miles every year compared to other car classes.

Most efficient large car

Tested economy: 68.9mpg

Claimed fuel economy: 85.6mpg

Engine: 1.8-litre petrol-hybrid, 120hp

Annual fuel cost: £747

Visit our guide to the most fuel-efficient large cars to see the model we’re talking about.

Least efficient large car: tied between the Lexus RC and the BMW 4 Series Gran Coupe

Tested economy: 33.6mpg

Claimed fuel economy: (Lexus) 39.2mpg, (BMW) 44.8mpg

Engine: (Lexus) 2.0-litre petrol, 242bhp, (BMW) 2.0-litre petrol, 245bhp

Annual fuel cost: £1,531

Difference between the most and least efficient medium car: £784 a year.

To find out which are the most efficient models for the other six car classes we cover, including large SUVs, people carriers (MPVs)luxury cars and estates, head to our guide to the most fuel-efficient cars we’ve tested.

Which? fuel cost calculator

We’ve based the calculations above on the average fuel prices from 2016: petrol at 109.2 pence per litre and diesel at 109.7 pence per litre.

But fuel prices are rising. If you want to do your own calculations, head to our free online fuel-cost calculator in our guide to how to choose between petrol and diesel.

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