Best and worst – mpg

• Most and least expensive cars to fuel
• How could you save more than £18k?
• Consider other running costs, too

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How much could you save on fuel bills by downsizing from a Bugatti Veyron to a Smart 0.8 CDI?

It's unlikely that you'll be making such an extreme switch, but your choice of car can have a dramatic impact on your fuel bills, even if you stick within the same class.

We're going to illustrate the point here in every sector, showing the difference in fuel bills over a typical three-year ownership period with 36,000 miles covered (a distance that a Veyron is highly unlikely to cover in its lifetime).

We'll explore the difference between the best and worst diesel version in each class as well as the best and worst petrol. We'll also show how big the difference in fuel bills are between the best diesel and the worst petrol.

Our comparisons are based on average fuel prices of £1.27 a litre for petrol and £1.31 a litre for diesel.

All of the comparisons are also based on the official average mpg. It's not a perfect system - you're unlikely to get within 10% of the figure in the real world – but at least it's a level playing field.

There's more to life than fuel costs
Don't forget, though, there's more to the running costs of your car than fuel. Depreciation plays a massive role in how cost-effective your car will prove to be over three years, so always remember to factor that in, along with insurance, servicing and tax costs.

To help you with your sums we've produced a petrol versus diesel calculator into which you can punch the numbers to find out which car really will cost you less over three years and 36,000 miles.

You can also easily weigh up the total three year costs with a three-way comparison.

Superminis
Best and worst petrol
Best: Fiat 500 TwinAir Sport 68.9mpg, £3010
Worst: Renault Modus 1.6 VVT Dynamique Auto 37.1mpg, £5589
Potential petrol saving: £2579

Best and worst diesel
Best: Smart Fortwo 0.8 cdi – 85.6mpg, £2502
Worst: Alfa Romeo Mito 1.6 JTDm Lusso 58.9mpg, £3637
Potential diesel saving: £1135

Potential saving between best diesel and worst petrol: £3087
Potential saving between best petrol and worst diesel: £627

Small family cars
Best and worst petrol
Best: Toyota Auris 1.8 VVT-i HSD 74.3mpg, £2791
Worst: Volvo S40 2.5 T5 R-Design Auto, £6604
Potential petrol saving: £3813

Best and worst diesel
Best: Audi A3 1.6 TDI 105 Start/Start, Seat Leon 1.6 TDI 105 S Ecomotive, Skoda Octavia 1.6 TDI CR Greenline II, Volkswagen Golf 1.6 TDI 105 Bluemotion, Volvo C30 1.6D DRIVe ES Start/Stop, Volvo S40 1.6D DRIVe SE Lux Start/Stop 74.3mpg, £2883
Worst: Renault Megane 2.0 dCi Privilege Auto 42.8mpg, £5005
Potential diesel saving: £2122

Potential saving between best diesel and worst petrol: £3721
Potential saving between best petrol and worst diesel: £2214

Family cars
Best and worst petrol
Best: 1.4 TSI 122 47.9mpg, £4329
Worst: Vauxhall Insignia 2.8T V6 25.7mpg, £8068
Potential petrol saving: £3739

Best and worst diesel
Best: Volkswagen Passat 1.6 TDI 105 Bluemotion 65.7mpg, £3260
Worst: Citroen C5 3.0 HDi V6 Exclusive Auto 38.2mpg, £5607
Potential diesel saving: £2347

Potential saving between best diesel and worst petrol: £4808
Potential saving between best petrol and worst diesel: £1278

Compact executive
Best and worst petrol
Best: BMW 318i 44.8mpg, £4629
Worst: Lexus IS F 24.8mpg, £8361
Potential petrol saving: £3732

Best and worst diesel
Best: BMW 320d Efficient Dynamics 68.9mpg, £3109
Worst: Audi 3.0 TDI quattro 42.2mpg, £5076
Potential diesel saving: £1967

Potential saving between best diesel and worst petrol: £5252
Potential saving between best petrol and worst diesel: £447

Executive
Best and worst petrol
Best:Infiniti M35 Hybrid, Mercedes E200 CGI Blue Efficiency 38.7mpg, £5358
Worst: Cadillac CTS-V 18.5mpg, £11,209
Potential petrol saving: £5851

Best and worst diesel
Best: Volvo S80 1.6D DRIVe 62.8mpg, £3411
Worst: Chrysler 300C 3.0 CRD V6 34.9mpg, £6138
Potential diesel saving: £2727

Potential saving between best diesel and worst petrol: £7798
Potential saving between best petrol and worst diesel: £779

MPV
Best and worst petrol
Best: Skoda Roomster 1.2 TSI 49.6mpg, £4181
Worst: Chrysler Grand Voyager 3.8 V6 23.0mpg, £9016
Potential petrol saving: £4835

Best and worst diesel
Best: Skoda Roomster 1.2 TDI CR Greenline II 67.3mpg, £3183
Worst: Ssangyong Rodius 270 28.8mpg, £7438
Potential diesel saving: £4255

Potential saving between best diesel and worst petrol: £5833
Potential saving between best petrol and worst diesel: £3257

Crossover
Best and worst petrol
Best: Toyota Urban Cruiser 1.33 VVT-i 51.4mpg, £4034
Worst: Volvo XC60 3.0 T6 26.4mpg, £7855
Potential petrol saving: £3821

Best and worst diesel
Best: Nissan Qashqai 1.5 dCi, Suzuki SX4 1.6 DDiS, Toyota Urban Cruiser 1.4 D-4D 57.6mpg, £3719
Worst: Ssangyong Kyron 2.7 SPR Auto 29.7mpg, £7212
Potential diesel saving: £3493

Potential saving between best diesel and worst petrol: £4136
Potential saving between best petrol and worst diesel: £3178

4x4
Best and worst petrol
Best: Lexus RX450h 44.8mpg, £4629
Worst: Jeep Grand Cherokee 6.1 V8 SRT-8 17.5mpg, £11,849
Potential petrol saving: £7221

Best and worst diesel
Best: Saab 9-3X 1.9 TTiD 55.4mpg, £3866
Worst: Mercedes GL450 CDI 24.4mpg, £8779

Potential diesel saving: £4913

Potential saving between best diesel and worst petrol: £7983
Potential saving between best petrol and worst diesel: £4150

Luxury
Best and worst petrol
Best: Audi A8 3.0 TFSI 31.0mpg, £6689
Worst: Bentley Continental Flying Spur 16.6mpg, £12,492
Potential petrol saving: £5803

Best and worst diesel
Best: Audi A8 3.0 TDI 42.8mpg, £5005
Worst: Range Rover 4.4 TDV8 30.1mpg, £7116
Potential diesel saving: £2111

Potential saving between best diesel and worst petrol: £7487
Potential saving between best petrol and worst diesel: £427

Coupe
Best and worst petrol
Best: Honda CR-Z 1.5 i-VTEC 56.5mpg, £3670
Worst: Bentley Continental GT 17.0mpg, £12,198
Potential petrol saving: £8528

Best and worst diesel
Best: BMW 118d 62.8mpg, £3411
Worst: Renault Laguna 3.0 V6 dCi GT 39.2mpg, £5464
Potential diesel saving: £2053

Potential saving between best diesel and worst petrol: £8787
Potential saving between best petrol and worst diesel: £1794

Performance
Best and worst petrol
Best: Mini Cooper 1.6 48.7mpg, £4258
Worst: Bugatti Veyron 10mpg, £20,736

Potential petrol saving: £16,478