Petrol vs diesel: which is best?

Which fuel should I go for? Let our petrol vs diesel guide answer all your questions on emissions, economy, depreciation and more

BuyaCar team
Jan 31, 2021

The battle between petrol and diesel has been going on for decades. Their mechanical differences are complex and even working out which option will cost you less overall is tricky, since new diesel cars typically cost more than equivalent petrol models, but offer the prospect of lower fuel bills - saving those who cover the highest mileages the most.

Meanwhile, petrol cars are typically noticeably more refined and can be cheaper to maintain. Then there's the perception that diesel cars are much more polluting than petrol models, when the reality is that petol models typically emit more of certain pollutants while diesels emit more of others.

All in all, there are lots of factors to take into account when making the choice between whether to grab a car that fuels at green fuel pumps or black ones, meaning that the decision of whether to go for petrol or diesel has never been so tough. Nowadays, you also have the option of heading down the electrified route, with a growing choice of mild hybrid, hybrid, plug-in hybrid and fully electric models pouring out onto the market.

Although electric and hybrid cars are beginning to gain traction in more mainstream markets, petrol cars at least are continuing to sell strongly. The story reads slightly differently for diesel cars, however.

Diesel gate - the scandal over real-world diesel emissions - rising fuel prices, the introduction of ULEZ and increased awareness of the harmful emissions produced by older diesel models, have all attributed to the collapse of diesel sales over recent years, with the share of new cars made up by diesel models dropping dramatically over the last five years.

Manufacturers have invested heavily in cleaning up diesel engines and reducing the amount of emissions they produce - with diesels typically emitting notably lower levels of CO2 than equivalent petrol models - but whether their reputation is harmed beyond repair remains to be seen.

Despite all of this doom and gloom, there are still plenty of reasons why a petrol or diesel car could still be the best option for you. We have all the arguments for which is best right here, so read on for more details.

 More reliable for short and slow journeys✔ Cheaper to run for high-mileage drivers
 Cheapest to buy✔ Best for heavier cars and towing
 Sportier performance✔ More economical than petrol
 Less fuel-efficient than diesels✘ More expensive to buy than petrol cars
 Power not as instant✘ May be unreliable if only used for short, low-speed trips
 Lacks pulling power for towing✘ Older diesel cars will be hit with surcharges


Choosing between petrol and diesel power

In short, diesels are more expensive to buy, and to tax, but offer better fuel economy. They also provide better pulling power - the shove that you feel when you move away. This makes them well-suited to towing, and powering heavy vehicles. Petrols are cheaper to buy and tax, but are less fuel efficient.

Generally, you’ll have to cover around 15,000 miles a year for the fuel savings of a diesel to outweigh its higher purchase cost.

Emissions are less easy to gauge. Diesels generally emit less carbon dioxide (CO2) than petrol models, but most models produce higher levels of other toxic pollutants.

Petrol and diesel running costs

Petrol vs diesel costs

  • Higher-mileage drivers may find that they can make significant fuel savings with diesel.
  • Petrol will remain best for low-mileage drivers because of the higher cost of diesel cars.
  • Buyers can protect themselves from uncertain future values with PCP and finance deals.
  • Surcharges for high emission vehicles entering cities will become more prevalent across Britain, affecting diesels more than petrol cars.

The price of a litre of diesel now costs more than £1.30 and petrol is over £1.20, according to RAC Fuelwatch, which monitors prices across the country. Those are around 10p per litre higher than a year ago, but a little cheaper than at the end of last year.

If you're wondering how to predict changing prices, then the answer is that you can't. Currency fluctuations, international sanctions and tax changes are just some of the factors that can cause prices to surge or slump.

It means that if there's little difference in the cost of running a petrol or diesel car, then it's not worth basing your decision solely on a small saving. On the other hand, if the price difference is large, then this is worth taking into consideration.

Purchase price and future value

Despite a fall in demand, diesel cars are usually between £500 to £2000 more expensive than their petrol counterparts.

But because they typically use less fuel and have lost value at a slower rate than petrol cars, that difference has often been cancelled out or even reversed.

The fact that diesels have held their value well has been particularly important because this has helped to make finance payments affordable. Repayments for the most popular type of finance, PCP, are based on the value that a car is expected to lose during the agreement.

However, Cap hpi, which predicts used car values, has highlighted that that diesel cars lost value (depreciated) faster than expected. In the first nine months of 2017, an average three-year-old diesel car lost 10.5 per cent of its value, compared with an expected figure of 8.5 per cent. In contrast, petrol car depreciation was at a record low.

As diesel sales continue to fall and cities start to introduce low emission zone charges, it's not known how diesel car prices will be affected.

You can protect yourself against an unexpected drop in value by taking out a PCP finance agreement or leasing a new car. You can hand the car back at the end with nothing more to pay, even if the vehicle has lost value at a faster rate than expected.

Diesel tax and surcharges

Low emissions zone sign

Running new and used diesel cars has become more expensive and will continue do to so for many drivers, thanks to tax changes and new charges for diesel cars in some low emission zones.

London has begun operating its ultra low emission zone (ULEZ) in the centre of the capital, with daily charges of £12.50 for the majority of diesel drivers. Other cities, including Birmingham, are preparing to follow next year.

Some local authorities are also introducing higher parking charges for diesel owners. You can read about the different proposals in detail, in our guide to diesel taxes and surcharges. The main points are below:

  • If you drive in central London, a diesel car could prove expensive. Most that were on the road before September 2015 don't meet the latest emissions standards and are affected by the ultra low emissions zone (ULEZ) fee of £12.50 per day. More details
  • Cars that don't meet the latest emissions standards (known as Euro 6) are also more likely to be affected by future clean air zone charges in other British cities. Some authorities are also imposing diesel parking surcharges. Find a Euro 6 car, which includes every new model registered since September 2015, and you have a better chance of avoiding future charges More details
  • The first year of car tax for brand new diesel cars is higher than for petrol vehicles, and the difference can be £300 or more (it's included in the purchase price).
  • Lower carbon dioxide (CO2) emissions from diesel cars has led to lower company car tax, but the Chancellor has increased the surcharge that business users pay, reducing the attractiveness of diesel.

Petrol or diesel: performance and economy

Aside from cost, there's also the engine's performance to consider. Diesel engines often feel more powerful than petrol engines because you don’t have to rev the engine hard to get the best performance. This makes them great for towing and powering big cars like SUVs. Many of the very latest cars are also considerably cleaner than those that went before them.

However, petrol engines tend to be quieter. With more power available the higher they are revved, these engines feel sportier to drive and often produce an agreeable growl from the exhaust.

Petrol vs diesel emissions

Diesel cars may emit less carbon dioxide (CO2) than petrol models, but they pump out higher levels of other pollutants, including nitrogen oxides (NOx) and tiny pieces of soot called particulates. They are blamed for up to 40,000 early deaths in Britain each year.

That's the reason why diesel vehicles are being targeted as part of efforts to reduce air pollution. The latest emissions regulations should have made diesel cars as clean as petrol versions, but several studies have shown that diesels are still considerably dirtier in real-world driving.

The situation is improving - some brand new diesel cars have recorded low levels of emissions, and a new official European test is being introduced later this year, which will ensure that new cars produce low levels of NOx when driving on public roads.

While you wouldn't want to be stuck in a sealed room with a petrol car running, their exhaust gases are cleaner and have fewer harmful pollutants.

Petrol or diesel for low mileage drivers

If your next car is only going to be used for low-speed journeys - across town, for example - then it’s almost always best to opt for a petrol car. In these cases, a petrol car is likely to be cheaper anyway, but it’s also likely to be more reliable than a diesel car in these circumstances: modern diesels need regular high speed runs (on motorways or dual carriageways) to keep their systems working.

It’s because diesel engines produce higher levels of harmful emissions than petrol engines and these include particulates: microscopic soot particles that can embed themselves into lungs, where they can cause breathing difficulties. To reduce these emissions, modern diesel car exhausts are fitted with diesel particulate filters (DPFs), which trap the harmful particles. When these filters are full, the trapped particles need to be burnt off.

The car’s onboard computers recognise when this is needed and change the engine settings so that the exhaust gas is hotter than usual. This is easily done when driving at high speeds, but can be impossible during town driving. That’s why the filters in low mileage cars often get clogged, requiring a visit to the dealer and sometimes costly repair work.

Petrol vs diesel performance on the road

Diesel-powered cars used to be renowned for being slow, rattly and smoky. Not anymore. You might hear a bit more of a clatter when you start a modern diesel engine but it sounds little different to a petrol motor when you’re on the move.

Many drivers prefer the way that diesel cars feel to drive. They produce most of their power at low engine revs, which means that they accelerate strongly almost the instant that you press the accelerator - petrol engines usually need revving to deliver maximum power.

However, there is a new generation of petrol engines becoming available, which provide many of the benefits of diesel engines with fewer drawbacks. These engines are turbocharged, to provide more power with good fuel economy, and are also powerful without having to be revved.

These include Ford’s small 1-litre petrol engine that’s fitted to cars including the Ford Fiesta (above) and Ford Focus, Nissan’s 1.3-litre petrol engine for the Nissan Qashqaiand the 1.5-litre petrol engine used in theMini Hatchback. You can rev these engines more than a diesel for extra power, which makes them feel sportier.

Fuel economy is closer to the level of diesel engines, and harmful exhaust emissions are also lower, although some tests suggest that these small turbocharged petrol engines release far more harmful nitrogen dioxide gas on the roads than laboratory tests permit.

Petrol vs diesel running costs calculated: Nissan Qashqai

Take a look at the example below, which is based on petrol and diesel prices remaining the same. If you’re covering 10,000 miles a year and want a best-selling Nissan Qashqai, then a petrol model will cost you less over three years. Drive 15,000 miles a year, though, and the efficiency of the diesel engine makes up for the higher price - just - making this model the cheapest option.


List price

Fuel economy

Value after 3 years

Running costs (10,000 miles / yr)

Running costs (15,000 miles / yr)

Nissan Qashqai Tekna 1.2 DIG-T 115 (petrol)






Nissan Qashqai Tekna 1.5 dCi 110 (diesel)






This example is based on the car’s fuel costs and loss of value over three years, according to Cap hpi. Other running costs such as road tax and servicing aren’t included, and neither are new car discounts, which can affect the calculations. We’ve used official mpg figures which are good for comparing the fuel efficiency of different cars but are higher than you’ll see in real-world driving.

Should you choose hybrid or electric power instead of petrol or diesel?

Hybrid and electric cars are becoming increasingly affordable, more suited to long journeys and ever-more efficient. If fuel prices remain high, then you could make impressive savings. All bring large benefits for business users, as they have lower carbon dioxide (CO2) emissions, which results in reduced company car tax.

Pure electric cars are the top eco choice with no exhaust emissions and cheap electricity top-ups, particularly if you plug in at home. The range of cars on a single charge is rapidly improving; the latest Nissan Leaf can cover more than 135 miles before the batteries dip alarmingly low, and the new Jaguar I-Pace (above) will go beyond 200 miles. Smaller cars, including the Renault Zoe will cover at least 100 miles before needing to be recharged. Electric cars are ideal for short distances but, due to their slightly higher purchase price, are more likely to offer savings to long-distance commuters, particularly if they can recharge at work.

Plug-in hybrid cars can also bring substantially lower fuel costs, but only for shorter journeys of between 20-25 miles. When fully charged, these vehicles can typically cover that distance on electric power alone. After this, a petrol or diesel engine takes over; the more this is used, the less you'll save, compared with a conventional car. Not everyone can save with these cars, due to their higher purchase price and limited electric range.

Standard hybrid cars can be little more expensive than a standard model, but bring reasonable fuel savings; particularly in stop-start traffic. They can't be plugged in, and so the batteries are recharged by recovering energy that would usually be lost during braking. The engine is also used for recharging when it's efficient to do so. The electricity drives a motor for power at very low speeds and to assist a standard petrol or diesel engine during acceleration. Long journeys at steady speeds don't play to the strengths of a hybrid system, as there's little energy to recover.

Whether an electric car is right for you will depend on the type of driving you do and whether you can take advantage of a reliable charging socket at work or at home. You can get fast wall chargers installed at home by a number of providers to help speed things up should needs be.


Latest car buying advice

  1. What is a car finance broker?

  2. Car finance for drivers with a provisional licence

  3. SUVs vs MPVs