/ Motoring

Petrol vs diesel – which fuel is cheapest in the long run?

It’s hard to ignore the incessant sky-rocketing prices at fuel stations – diesel has tipped over the £1.50 a litre mark on many forecourts. With petrol 7p cheaper a litre, is diesel now a no-go?

With no sign of a let up in fuel price– and the possibility of a 3p fuel tax increase in August to rub salt into the wound – is now the time to ditch your diesel and go for an efficient petrol-engine car instead?

Although the 7p difference between petrol and diesel may not sound like much, it equates to nearly £4 more every time you fill up. For example, a Ford Focus hatchback with 55-litre fuel tank will cost you around £80.19 to fill up with diesel, but £76.34 with petrol.

If you only fill your tank up twice a month, it looks like you’ll be losing out on over £90 a year with diesel.

The cost of filling up my car

Even the cost of filling up a small car has gone up by more than a third over the past few years. As the price indicator on the fuel pump ticked swiftly past £60 when I was filling up my Renault Modus last night, I winced and was sorely tempted to stop – how could a supermini cost that much to fill up?

Yet, I’m still better off than plenty of other motorists right now. Why? Because my Modus has a petrol engine. If it had a diesel, it’d have cost at least £3 more.

So should I be smug about my fuel choice, or does the old adage about diesel cars being cheaper in the long run still hold true?

Having plugged the relevant info on my car’s purchase price, mpg, annual mileage and fuel price per litre into our clever petrol vs diesel calculator, I don’t really have that much to be happy about.

Does diesel pay in the long run?

Even with the current painfully high diesel prices, in just under two and a half years I’d be able to recoup the extra cost of filling up a diesel car over a petrol one. I’d even be able to recoup the extra cost of buying a diesel model.

Why? Because despite all the extra costs that come with diesel models, they always do more miles per gallon than petrol ones. For example, the 1.6 petrol Ford Focus averages 47.1mpg, compared to the 1.6 diesel stretching to 67.3mpg.

I drive over 12,000 miles a year, so spend an awful lot on fuel, That means going for a diesel model may well actually save me money in the long run, despite current prices. I’m certainly tempted.

If you’re thinking of buying a new car, how much are the current eye-watering fuel prices affecting your choice of diesel or petrol car?


I am planning to change my car in the next year and will have to decide on whether to stick with diesel or switch to petrol. My first diesel car was bought in 2002 when the main dealer was offering new Golf diesels at the same price as petrol models and the offer was too good to miss. My present diesel Golf was another new car that the dealer offered a good discount on, presumably to make way for new stock.

I would prefer to stick to diesel, but I drive only 7000 miles a year. What I buy will depend on what is on offer. I am not in any hurry to change my car and I will keep an eye on what is available from local dealers, whether that is petrol or diesel.

You’ve missed one essential consideration…depreciation. If you add up cost of ownership over a period, you’ll find that depreciation on anything but the oldest cars makes all other factors, including fuel costs, pretty insignificant for most drivers. (Insurance could be an even bigger hit for the young).

Most diesel cars depreciate more slowly than their petrol equivalents, reflecting their tendency to be longer-lived and (b) fuel cost is an even greater consideration for anyone buying an older car.

There are other things to take into account too, such as cost of servicing.

When replacing my car, I put together a simple spreadsheet to calculate cost of ownership of all the cars I’m considering. It includes factors such as cost of money (interest on a loan and/or loss of interest on capital), depreciation, road fund licence, insurance, servicing and fuel. The results are often surprising.

Keith Merry says:
16 March 2012

Can anyone please tell me why diesel in the UK is more expensive than petrol… Other countries that I have visited it has always been that diesel is cheaper than petrol..Are we being ripped off again?

Colin Samson says:
19 March 2012

The excuse for higher UK diesel prices is to do with lack of UK diesel refinery capacity. The UK cannot refine enough diesel for domestic supply, so has to import some refined diesel; this is more expensive. It seems that we are the victims of the recent success in UK sales of diesel cars; more refineries are needed but the fuel companies don’t want to spend the money required to build more . . . just yet.

D M L says:
17 June 2013

I am sorry to say I am old enough to remember when diesel was a lot cheaper than petrol in the uk but as more diesel cars became available, guess what, up went the price of diesel and it has never been below petrol again , can anyone confirm that diesel is actually cheeper to produce than petrol? or is Keith Merry correct it is yet another case of keep quiet and we will rip you off.

Robrt J Tucker says:
16 March 2012

No matter what we the motorists plan..albeit petrol or diesel ;.the Government will swap about to keep that which makes most revenue for the Government. if people stop buying Diesel.the Government will bump up the petrol prices..if we continue to use diesel the price will increase..to maintain revenue…
the answer is get 20 petrol or diesel Customers and buy up a block stock of either….or maybe get 50 motorists to block reserve a stock at bulk prices from the Oil Companies….I’m sure that will beat the Tax man..

For many years diesel was significantly cheaper than petrol, then overnight Diesel suddenly became much more expensive.

I think we need to look at why this sudden change came about and why non commercial Diesel is so expensive. I think at the time the Govt said that drivers of Diesel cars were gaining by having a higher MPG and to have cheap fuel as well was too much of a good thing.

I have just purchased a small diesel car for my wife with the sole intention of running it on cooking oil, which is considerably cheaper.

Top Driver says:
16 March 2012

You are falling into the trap that manufacturers want us to by quoting official fuel consumptions. The majority of motoring magazines do the same which makes their cost comparisons meaningless. In the real world official figures are pure fantasy. To use your example, I run a 1.6 diesel focus which has done 12,000 miles so is well run in yet even with gentle driving and 65mph cruising on motorways I only get 52mpg – nowhere near Ford’s claimed 67mpg. I prefer the superior pulling power of diesels but am seriously thinking of switching back to petrol but, for the reasons given above, i find it impossible to make any kind of true cost comparison.

David says:
16 March 2012

“If you only fill your tank up twice a month, you’ll be losing out on over £90 a year with diesel”.

Nonsense. You won’t need to fill it up as often. 12,000 miles at 47.1mpg with petrol at £1.43 a litre will cost you £1656. Switch to diesel at £1.50 a litre, but with 63.7mpg and you’ll only spend £1284. A saving of £372.

Hello David, you’re right as Claire goes on to explain – diesel is better in the long run. We’ve made a quick edit just to avoid confusion for those who don’t get to the end of the Convo. Thanks.

Let’s ignore pricing, taxation and engine/car efficiency for a minute and think about these fuels purely as a source of energy.

Both petrol and diesel have similar calorific values – about 46 MJ/kg depending on the blend. BUT, petrol weighs 5%-15% less that diesel. Because both fuels are sold by volume, not weight, you actually end up with 5%-15% less energy for your money when you buy petrol.

This is one of the reasons why diesel cars use “less” fuel, when measured in MPG. If we measured fuel by weight, the diesel car would not outperform the petrol version by such a large margin.

As long as fuel is sold by volume, you should expect diesel to cost up to 10% more than petrol and be happy to pay the price, as you are still getting more energy per £.

Whether manufacturers need to change more for building and servicing diesel models is a separate debate. Given the enormous economies of scale in motor manufacturing, I suspect functional pricing is at work.

Meant to write: ” … need to charge more … “.

Anyone considering changing their car with fuel consumption in mind should take a look at the Real Life Fuel Economy Register on the Honest John web site ate http://www.honestjohn.co.uk/realmpg/
This takes input from many drivers on their real world fuel consumption and gives a much better guide than manufacturers’ figures. The more of us who use it, the better its data become.

Long distance trabnsport – trucks – historically used Diesel (and still do) because diesel is more efficient for such usage. It also makes sense for cars where many journeys are long.

For the driver who does predominantly short journeys, diesels will not get their particle filters sufficiently hot unless they go through a cleaning cycle which wastes loads of fuel. They are better off with an efficient petrol hybrid car.

This is getting tedious…we should fret about depreciation and reliability long before fuel consumption (although depreciation is less important for older, low-value cars).

Variations in fuel costs are generally insignificant against depreciation and the cost – not to mention inconvenience – of breakdowns and repairs.

If you keep a car for ten years or more, depreciation is not a very important factor in running cost. Unless you are unlucky, breakdowns and repairs should not be a significant cost if cars are properly serviced – provided that you avoid makes/models that are known to be unreliable.

I think you’ll find that, if you keep a car 10 years, you’re in a very small minority. Even if you do, and it’s, say, a £20,000 car, it may be worth nothing after 10 years or it may be worth something like £3000, depending on what you buy. Choose the right one and save £300 p.a. which could easily compensate for higher fuel costs.

That isn’t to say fuel consumption is to be ignored, just that it isn’t the first priority. If you can find a car that depreciates slowly AND has top fuel economy, that’s perfect.

Regarding breakdowns and repairs, of course they SHOULDN’T be a significant cost, but the fact is that, with many cars, they ARE. And people do keep buying unreliable cars, despite the best efforts of Which? My present car, owned from new, is 6 years old and has needed nothing but routine servicing. My friend’s Saab cost him best part of £3,000 in repairs over 6 years – £500 p.a. pays for a lot of fuel. As for my neighbour’s Alfa and my daughter-in-law’s Fiat, the less said the better.

I may be in a very small minority but my strategy of buying new and keeping cars for a long time has worked well for me. Buying new means that I am not inheriting someone else’s problems.

If you have kept your car for six years and only paid for servicing you have probably saved a fair amount of money compared with those who have changed their car once or twice in that time.

New cars are more economical but I am reasonably happy that my 10 year old diesel gives around 48 mpg over the year, despite being used for a lot of short journeys. All I have paid for is to have a door lock changed and the front electric windows fixed, and I have done all my own servicing except for changing the timing belt.

I’m with Wavechange on this. My strategy is to buy new and we hold onto our cars for around 10 years. It’s only significant advances in vehicle safety that make for a compelling change – like airbags and ABS.

Whilst it is possible to estimate the total cost of ownership based on the various factors Dave mentions above, the one unknown is the cost of fuel, so why would fuel economy be any less of a consideration than depreciation? And, ignoring hybrids and other advanced fuel-saving technologies, is there any car with high fuel consumption that depreciates more slowly than the equivalent model with a more frugal engine?

I decided to make the switch from petrol to Diesel when fuel was 80p per litre. I’m now spending an extra £1000 every year I hadn’t reckoned on, but my car’s depreciation hasn’t changed at all – other than on paper – because I have no plans to sell, until it becomes uneconomical to run or repair.

I know my car will be worth next to nothing at the end of 10 years, but I still choose one that is supposedly reliable, with low depreciation – just in case I do need to sell it within a few years of purchase – but with good fuel economy too, as I suspect £2-£3 per litre isn’t too far off.

PaulJ says:
16 March 2012

Not all diesels are suited to short journeys. Vehicles fitted with DPF filters need to burn off the excess soot and they do this on runs where the revs are higher for at least 15 minutes, so that a high temperature is reached to remove the excess soot.
People who only do short journeys, or mainly town work should not buy a diesel if it has a DPF fitted.

Agreed – and if it doesn’t have a DPF fitted you shouldn’t buy it because the emissions on a cold start are cumulatively toxic and far more harmful than without (which is still far more harmful than petrol emissions. Measuring only CO2 is fallacious when it comes to determining the mastiness of emissions).

Also agree, but not neccesarily high revs needed. A higher exhaust system temperature through travelling further also achieves the temperature required.

Roerjp, with regard to your above comment do you mean ” Agreed-and if it DOES have a DPF fitted you shouldn’t buy it…?” Unless I am out of date my understanding is that the introduction of DPFs for all diesel cars has resulted from EU legislation which was NOT based on solid medical evidence ie the necessity for DPFs is unproven. Has this state of affairs resulted from vested interests of the motor industry? From what I read DPF’s do cause a lot of bother. Also,
Honest John in the Telegraph points out the extra potential costs of running EU5 diesel cars when they are 3 to 6 years old which include replacement DPF’s, replacement Duel Mass Flywheels, replacement Exhaust Gas Recirculation valves, replacement Turbo’s and replacement timing belts and tensioners.The independent garage which services my 11 year old Mark 4 petrol Golf ( owned since new) is no longer recommending diesel cars so I will probably replace with a new petrol car . Meanwhile it is great to have a car with minimal depreciation!

Dave – I am an asthmatic who is strongly affected by diesel fumes, and I know others who have the same problem. Fortunately, modern diesel vehicles are generally much cleaner than those that used to be on the road and I welcome any measures that will achieve further improvements.

Hi Dave.

I actually did mean what I said – for reasons Wavechange identified. The emissions from unfiltered Diesel engines, particularly when cold, are claggy – full of soot and nanoparticles. the nanoparticles may not in themselves be allergens, but they potentiate allergy from other things. I am a strong believer that the rapid expansion of diesel engines in private cars without filters has accelerated the upward trend in asthmatics over the last decade or two. The curves of the growth of diesels and growth of asthmatics correlate quite well over the nineties, but asthma flattened somewhat in the back end of the noughties – as PSV filters came of age.

I’m pleased to report that my BMW 520D, complete with DPF, 6 years old this month, has so far suffered none of these problems. In fact, it’s suffered no problems at all apart from a few irritating trim rattles and buzzes. I suppose I should be touching wood…


Another factor that has helped some asthmatics is considerable reduction in sulphur content of diesel. Even red diesel, which is used in boats and in many agricultural/industrial engines will have to be virtually sulphur-free from the start of this year. Sulphur dioxide in exhausts does not affect all asthmatics but it is a bigger problem than particulates for some of us.

The difference between diesel and petrol prices has widened recently because of the large increase in demand for diesel ; diesel cars now make up over 50% of all cars in the UK I believe
Refineries were not designed to produce such a large proportion of diesel so market forces have increased its relative cost.

Diesel engined cars still tend to produce less CO2 per kilometer than petrol versions though.

Essexman says:
18 March 2012

A couple of points not touched on so far here. As someone who suffered from asthma for many years of my life I can see the anti diesel case. But unleaded petrol contains benzene & toluene, two very powerful carcinogens, which are mostly burnt off by the catalytic converter – but only when it’s warmed up. And with diesel at least you are not carrying a tankful of explosive in your tank. The flashpoint of even premium diesel is approximately 50c, for petrol it’s around -40c. It doesn’t get that hot, or cold in the U.K.

You are right about the flashpoint of diesel and petrol, and there has been a move towards diesel for boats, encouraged by the number of fires. Unfortunately, the autoignition temperature of diesel is substantially less than for petrol. What worries me most of all is the use of LPG as fuel.

Both diesel and petrol are potentially harmful and we should all drive and use public transport as little as possible.

Leaf user says:
19 March 2012

Electric cars, while currently expensive to buy, are very cheap to run and at the tailpipe (there isn’t one) do not generate any the pollutants mentioned above. Now that we’ve owned a Nissan Leaf for 6 months, neither of us would go back to an internal combustion engine (ICE) car for everday use. As electric vehicle (EV) batteries improve and more fast chargers become available, the usual excuses for not buying an EV will become irrelevant.

Batteries have barely improved over the years that we have asked them to do more, what makes you think that battery technology will improve at a faster rate in the coming years?

So the usual drawbacks of an electric car still remain, and will remain for many years to come.

I personally don’t drive that much in the week so I have a petrol engine (mini cooper s). It is however a small engine, but fitted with a turbo so you can have economy or performance, whichever you prefer at the time.

I might actually be one of the only people in the world who doesn’t think petrol that expensive.

Having recently had an operation and had to travel around on buses and taxis, I have to say any car, petrol or diesel, is worth every penny that we pay. Add to that the fact that Mini gave me 3 free MOT’s and I bought their TLC servicing pack (3 years servicing for £270), plus free breakdown and recovery and that minis depreciate slowly, I definitely bought the right option, small car, petrol engine + turbo.


I am encouraged by the developments with laptop batteries in the last few years. At one time you had to be very careful about how to treat these batteries to get decent life and now it does not seem to matter. Well that is my experience with recent Mac laptops. It’s not all down to the batteries and the electronics that control charging and prevent over-discharging are also important.

I agree with your thoughts on fuel prices, even if no-one else does. One of the reasons that most of us avoid small cars is that we sometimes need a larger car. If it was as cheap and easy to hire a larger car as it was for me to do at work, I would certainly run a small car rather than a medium car.

Agree with wavechange about the importance of battery management. The batteries in my two current laptops have been brilliant, but I think that’s mainly down to my choosing the option of limiting battery charge to 80% of capacity. Trouble is, while that’s great for long-term battery life, it limits the running time. I can live with that, in my laptops, but the range of the Leaf is too restrictive for me, as it is, without restricting the charge to less than 100%.

Also agree about car size…I run a big estate car, mainly so that we can fit everything in two or three times a year for self-catering activity holidays. Most of the time, I curse the size of it, but I can’t justify running two cars.

I have been informed another problem with some diesel engines is that their inlet manifolds can “gum up “with a curious wax like material which can occur as early as 30,000 miles.(This sounds to me a bit like the manufacture of polythene from the polymerisation of the gas ethylene!) The symptoms include loss of power because of increasing restriction to gas flow.The cure is an expensive clean up of the cylinder head.Diesel Ford Focus and diesel Golfs are named vehicles.

Sorry,the above post should have read “that their cylinder heads can gum up….”

Peter says:
19 March 2012

Just a simple question: Why is the UK pricing of diesel at the pump (when compared with petrol) so out of kilter with fuel prices in Europe? In all European countries, the Petrol/Diesel pricing is opposite to UK with price difference for diesel/litre being 5p or so cheaper than petrol/litre .