Premium / regular / supermarket petrol - what's the difference?

[StewartR]

I usually fill up my car at the local Esso station. But yesterday I was on a long journey and there was a Tesco superstore at the location where I took a pit-stop, and I was running low, so I filled up there. I was astonished how cheap it was, and not for the first time it got me wondering about the difference between supermarket petrol, "regular" branded petrol, and "premium" branded petrol. So I did some research online, but I can't say I've got to the bottom of it.

What I think I've learned:
(1) "Premium"petrol has a higher octane rating, so will deliver more power and better fuel efficiency.
(2) The improved fuel efficiency you get with "premium" petrol is typically up to ~2% and won't justify the extra cost which is typically ~5%.
(3) Supermarket petrol and "regular" branded petrol will deliver the same performance/efficiency results because they both have to meet the same technical standards.
(4) Manufacturers say that "premium" petrol contains more additives (detergent etc) that "look after your engine", but the effect of such additives is not easily demonstrated / tested / proven.
(5) Some people say that supermarket petrol contains fewer additives, but again the effect is not easily demonstrated / tested / proven.

The whole issue about additives seems very murky to me. Some commentators have suggested that they are little more than a bit of marketing mumbo-jumbo like you get with shampoo and stuff like that. Certainly I'd have thought that, if the additives in "premium" petrol really did provide long-term benefits to your engine, it wouldn't be too had for the manufacturers to demonstrate this. Get a bunch of identical engines, run half of them continuously for a year on regular petrol, run half of them continuously for a year on premium petrol, and see what happens. It wouldn't be a cheap experiment but these are vast companies and they could easily afford it. And the fact that apparently none of them has done this suggests to me that perhaps they're not so confident of the outcome.

So anyway, can anyone help by expanding on this? As far as I can tell, (1), (2) and (3) are pretty solid, but (4) and (5) seem much more open to conjecture. Has anyone seen any reliable evidence of the effects of additives? (I'm not really interested in anecdotes, and I don't care whether somebody's Uncle Jim's car ran for 500,000 miles on supermarket petrol. I want to see the science.)

 

[Deleted member 49428]

Octane is a way to descripe the petrols "ability" to self combust under high pressure. Low octane will do so more readilly than high octane meaning high compression engines will need the high octane numbers and low compression ones wont

 

[john.margetts]

A few years who, Shell brought out a 'better' petrol which ended up damaging engines - both expensive and embarrassing for them.

Tesco petrol is refined by the big-name refineries (of which there are very few) so will be competently made. Actually, Tesco, as a major player in the field, will dictate high standards to the refinery. I have no experience of the petrol industry but worked for many years in food processing. Making Tesco labeled food for them meant us sticking to very stringent quality standards. Asda were even worse, checking cleanliness in the roof space of the factory.

 

[Mr Bump]

I think most of the time it is just mumbo jumbo and brands like shell and BP trying to justify charging more.

 

[ecoleman]

There is no difference between regular (branded) and supermarket fuel. The supermarket will shop around for the best price and it's cheap because it a loss leader. The cheap price drives customers to it's stores.

 

[Byker28i]

The base fuels are the same and have to meet a standard, whats different is the additives, which is how for instance Tesco polluted a large batch of their fuel with silicone causing cars to breakdown. They thought they could get away with selling the fuel rather than disposing of it at a huge loss. I won't touch Tesco's fuel.

Some supermarkets buy on the market, some have invested into refinaries/suppliers.

Some supermarkets use fuel as a loss leader, sell it at a very slight profit to get you into their stores as part of your weekly shop etc, hence the low price.
Some of the premium fuels, i.e. Shell vPower have a higher octane rating so you can tune performance cars to take advantage.


For economy, the biggest difference is the type/time of journey and your right foot

 

[Byker28i]

2007 - Tesco contaminated fuel scandal
https://en.wikipedia.org/wiki/2007_United_Kingdom_petrol_contamination

 

[welshwizard645]

The difference between Shell and Sainsbury's is quite remarkable on our 17 year old Golf, it's run more cleanly on Shell and the lambda sensor doesn;t get bunged up.

 

[Deleted member 49428]

BTW 2%!!! ............ In real life thats=0
The amount og data needed, the measurement uncertainty and the even slightest day to day differences etc. even in controlled environments makes such a claim hmm unserious

 

[nilagin]

Octane is a way to descripe the petrols "ability" to self combust under high pressure. Low octane will do so more readilly than high octane meaning high compression engines will need the high octane numbers and low compression ones wont

Are you sure about that? Petrol engines require spark to ignite the fuel not compression. Diesel fuel is ignited by high compression and has a cetane rating not octane.
There are higher compression petrol engines now due to running direct injection but it has nothing to do with fuel rating and no where near the compression ratio of diesel engines.
As the OP has stated a higher octane fuel will burn better. This leads to less carbon build up in the combustion chamber meaning less hot spots which can cause preignition. A higher octane rating means less likelihood of the ecu having to retard spark due to knock. Meaning a cleaner more efficient burn. The extra cost of higher octane fuel may not relate to the extra power and mpg you may get but the engine will remain cleaner as a result and perform better for longer. Emissions should also be better too. Whether other additives work I don't know but as they are part of the premium higher octane fuel you have no choice but to buy them. My current and previous cars will only run on 95RON as a minimum, not lesser fuels as found in some other countries. But I only run it on 98RON. Even if it wasn't a performance engine I would still run it on 98 as it's better for the engine in the long run.

 

[nilagin]

A few years who, Shell brought out a 'better' petrol which ended up damaging engines - both expensive and embarrassing for them.

Tesco petrol is refined by the big-name refineries (of which there are very few) so will be competently made. Actually, Tesco, as a major player in the field, will dictate high standards to the refinery. I have no experience of the petrol industry but worked for many years in food processing. Making Tesco labeled food for them meant us sticking to very stringent quality standards. Asda were even worse, checking cleanliness in the roof space of the factory.

All petrols come from the same refineries dotted around the country. The tanker drivers just select which ever mix of fuel and additive is required for the fuel station he is delivering to.

 

[Deleted member 49428]

Are you sure about that? Petrol engines require spark to ignite the fuel not compression. Diesel fuel is ignited by high compression and has a cetane rating not octane.
There are higher compression petrol engines now due to running direct injection but it has nothing to do with fuel rating and no where near the compression ratio of diesel engines.
As the OP has stated a higher octane fuel will burn better. This leads to less carbon build up in the combustion chamber meaning less hot spots which can cause preignition. A higher octane rating means less likelihood of the ecu having to retard spark due to knock. Meaning a cleaner more efficient burn. The extra cost of higher octane fuel may not relate to the extra power and mpg you may get but the engine will remain cleaner as a result and perform better for longer. Emissions should also be better too. Whether other additives work I don't know but as they are part of the premium higher octane fuel you have no choice but to buy them. My current and previous cars will only run on 95RON as a minimum, not lesser fuels as found in some other countries. But I only run it on 98RON. Even if it wasn't a performance engine I would still run it on 98 as it's better for the engine in the long run.

https://www.exxon.com/en/octane-rating

https://en.m.wikipedia.org/wiki/Octane_rating

 

[nilagin]

https://www.exxon.com/en/octane-rating

https://en.m.wikipedia.org/wiki/Octane_rating

Neither link says anything about the fuel self combusting (as you put it) due to compression and fuel rating. If that was the case why would they bother with spark plugs?

I am currently testing and developing a new engine at work. It has a slightly lower compression ratio than it's counterparts, but it will happily run on 91, 95 & 98RON fuel. The only difference being the power and torque it can achieve on each fuel. The figures are quite clos on 95 and 98 but with the latter the figures can be achieved on less boost and with less fuel.

 

[Deleted member 49428]

Neither link says anything about the fuel self combusting (as you put it) due to compression and fuel rating. If that was the case why would they bother with spark plugs?

I am currently testing and developing a new engine at work. It has a slightly lower compression ratio than it's counterparts, but it will happily run on 91, 95 & 98RON fuel. The only difference being the power and torque it can achieve on each fuel. The figures are quite clos on 95 and 98 but with the latter the figures can be achieved on less boost and with less fuel.

https://www.bellperformance.com/blog/bid/101182/What-Does-Octane-Do-In-Gasoline-Octane-Ratings
Actually the octane number descripe the mixture relateret the mix og Isooctane and n-heptane so 95 octan equals the proper tids og a mix og 95% ISO octane and 5% N-heptane.

 

[Uneducated_Rick]

So anyway, can anyone help by expanding on this? As far as I can tell, (1), (2) and (3) are pretty solid, but (4) and (5) seem much more open to conjecture. Has anyone seen any reliable evidence of the effects of additives? (I'm not really interested in anecdotes, and I don't care whether somebody's Uncle Jim's car ran for 500,000 miles on supermarket petrol. I want to see the science.)

VW used to recommend (until about 5 years ago at least) that their diesel engines be filled up with premium fuel 1 in 10, the language seemd to indicate that standard was fine most of the time but the engine occassionally needed a richer fuel to help clear it out (this might have been days before software hacks for the emissions).

In a previous job one of our clients were a petrol company, and our contact told me:

• what they sell to 1 supermarket is exactly the same as what they sold on their own forecourts
  
• most supermarkets had a different blend of additives
  
• at least 1 supermarket purchase their fuel from different suppliers in different regions so not all of their forecourts across the country were consistent
• certain petrol stations that aren't supermarkets, but nor are they companies who own refineries, buy their petrol from different suppliers depening who they can get a discount from that month

This company were convinced that there was enough data to prove a statistically significant difference between the different additives. When pushed for whether the difference was meaningful there wasn't much of a response.

 

[tijuana taxi]

When I towed a caravan my old 2 litre Cavalier lost some of its pulling power if I used Tesco petrol.
So whatever people said it definitely was different and tests I'm sure would have proved it

 

[omens]

My car will run on both 95 and 98 RON. On the latter, the mpg is better and there is a discernible difference in performance.

 

[Mr Bump]

I used to run my old Kawasaki z750 on super unleaded and it ran a lot better, smoother and more power.

 

[nilagin]

So by self combustion you actually meant pre-ignition or knock. But a higher octane rating will also mean a cleaner burn because the spark can run at it's optimum level of spark advancement. That's not to say all petrol engines should be run all the time on 98 if the engine hasn't been mapped for it but some 98 in the tank once in a while will clear any carbon build up on the piston and valves.

You could still run a high compression engine on 91 but the spark would likely be heavily retarded and the boost would have to be restricted to reduce the chances of knock and the engine output would be reduced as a consequence. But we only have 95 and 98 RON in the UK so 91 RON is not a concern and most engines will run on 95 RON as a minimum and as I said not all will get a performance increase from 98RON but occasional use will help keep the combustion chamber free of carbon build up.

 

[Dave *]

My car will run on both 95 and 98 RON. On the latter, the mpg is better and there is a discernible difference in performance.

Same here, and that’s on a bog standard Focus 1.6, there’s a clearly discernible difference in use.

 

[noneforit]

In my experience, the only difference is the cost.

Perhaps having a super car might make a difference but in 12 years of driving and owning 10 cars, I have noticed naff all difference between any of it, from a performance point of view or from a MPG perspective.

I am sure Science would say otherwise but real world, I have never seen a difference.

To be fair, I just fill up and don’t worry about the MPG so maybe it does make a slight difference but I am still considerably poorer every month

 

[Byker28i]

My car will run on both 95 and 98 RON. On the latter, the mpg is better and there is a discernible difference in performance.

Same here, and that’s on a bog standard Focus 1.6, there’s a clearly discernible difference in use.

On what mileage/type trip?

My car is tuned for 99 octane (shell vpower) but if I run it on other lower grade fuel I can reset the adaptives to let it better modify it's settings to cope. I suggest your engines are doing the same in todays modern ECU's. 98 octane fuel will give a better 'bang' so there will be a slight better performance, so it's possible on a long run that maybe you aren't having to put your foot down more up hills etc.

I know getting our diesel car mapped increased the mpg on long runs by a just a few, but it won't be cost effective for a long time as I worked out it was about 40,000 miles of long runs, not the short or normal journeys, so realistically the lifetime I have the car. It is fun however having the extra grunt

 

[nilagin]

Same here, and that’s on a bog standard Focus 1.6, there’s a clearly discernible difference in use.

My son had a Focus 1.6. He did some work experience with an engine builder at a small race team. They used to fill his tank up with race fuel from time to time as payment. He reckons the engine was so much livelier on that.

A ot of cars will be mapped to run on both 95 and 98. But most people will only run them on 95 as it is cheaper. I could run mine on 95 but it would lose out on performance and it's only about £3 extra a week at the most to run it on 98.

 

[omens]

On what mileage/type trip?

Both motorway miles and general town. I've even noticed differences with Tesco's 99-RON Momentum stuff and Shell's V-power. Tescos gave better mpg over a 300mile return journey. V-power made the car feel more aggressive or responsive when driving.

 

[Deleted member 49428]

So by self combustion you actually meant pre-ignition or knock. But a higher octane rating will also mean a cleaner burn because the spark can run at it's optimum level of spark advancement. That's not to say all petrol engines should be run all the time on 98 if the engine hasn't been mapped for it but some 98 in the tank once in a while will clear any carbon build up on the piston and valves.

You could still run a high compression engine on 91 but the spark would likely be heavily retarded and the boost would have to be restricted to reduce the chances of knock and the engine output would be reduced as a consequence. But we only have 95 and 98 RON in the UK so 91 RON is not a concern and most engines will run on 95 RON as a minimum and as I said not all will get a performance increase from 98RON but occasional use will help keep the combustion chamber free of carbon build up.

Yes correct, sorry for my bad english. In DK er have 92 and 95. 98 disapeared years ago.

 

[Dave *]

My son had a Focus 1.6. He did some work experience with an engine builder at a small race team. They used to fill his tank up with race fuel from time to time as payment. He reckons the engine was so much livelier on that.

A ot of cars will be mapped to run on both 95 and 98. But most people will only run them on 95 as it is cheaper. I could run mine on 95 but it would lose out on performance and it's only about £3 extra a week at the most to run it on 98.

It’s not just performance, the engine seems to run smoother especially at lower revs. It’s quite noticeable when accelerating in 2nd or 3rd from very low revs, the lower octane fuel will cause knocking/pinking as the revs climb while the premium fuel just pulls smoothly.

 

[Deleted member 49428]

Both motorway miles and general town. I've even noticed differences with Tesco's 99-RON Momentum stuff and Shell's V-power. Tescos gave better mpg over a 300mile return journey. V-power made the car feel more aggressive or responsive when driving.

I never experienced any difference between regular 95 and v-power in our 2009 1,4 TSI powered Octavia. But the kids enjoyed the Lego cars

 

[Byker28i]

My son had a Focus 1.6. He did some work experience with an engine builder at a small race team. They used to fill his tank up with race fuel from time to time as payment. He reckons the engine was so much livelier on that.

A ot of cars will be mapped to run on both 95 and 98. But most people will only run them on 95 as it is cheaper. I could run mine on 95 but it would lose out on performance and it's only about £3 extra a week at the most to run it on 98.

Not surprised, race fuel is 104 octane upwards. You should see the flames out the TVR on that, but then that is ridiculously expensive.

Are ECU's mapped for both, or just run adaptives /wide band lambdas that cope?

 

[StewartR]

Wow. I sometimes wonder whether this forum should really be called "Talk Motors", because any thread vaguely related to cars seems to get so much attention.

But so far there's a noticeable lack of consensus, and a heavy preponderance of anecdote. Plus, probably, a fair smattering of confirmation bias.

Let's not worry about the 95/98 RON thing. There are obvious reasons why higher octane fuel will lead to better combustion, and the benefits in performance and efficiency are real. No need to debate that.

I'm not interested in performance though. I drive a car because I have to, not because I want to. I have a 2009 VW Golf 1.4 TSi DSG, about as dull a car as you could imagine. So I'm not going to buy "premium" fuel for performance reasons. I'm not interested in smoother running either, because my engine always runs smoothly. I have *never* heard any kind of knocking from it.

But I am interested in fuel efficiency and I am interested in longevity.

If anyone can point to any reliable evidence regarding fuel efficiency, that would be very welcome. There doesn't seem to be much. BP claims its Ultimate unleaded "could give you up to 21 miles per tank" - an improvement of about 5%, the way they've calculated it - but it's not at all clear how they're doing the comparison so it's pretty worthless. Esso claims its Suprteme+ unleaded "helps to improve your fuel economy" but doesn't provide any numbers. Shell claims absolutely nothing on a page that's peppered with "no guarantees". It seems almost certain that - for people driving dull cars like mine, at least - the cost of premium fuel isn't going to be justifiable in terms of improved efficiency.

And I'm really really interested in any reliable evidence about additives helping to prolong engine life. As I said earlier, you'd think it would be straightforward to test, so the fact that there don't seem to be any tests is suspicious.

Can anyone else point to actual quantitative evidence in either of these areas?

 

[Dave *]

If your car drives in a manner that you are satisfied with why does it matter?

 

[Mr-Incy]

I have a Fiesta ST, a few years ago I went from using regular petrol to premium and in all honesty never really noticed the difference. I do a mix of country, city and motorway driving.
I went back to using regular, although the price difference isn't huge, I just didn't see the point in using the premium.... I have also noticed that a number of garages don't offer any premium petrol, there is a Sainsburys near me that only has regular unleaded and diesel at the pumps.

 

[Mr Bump]

my chainsaw goes a lot faster on the super unleaded

 

[AJQS]

Ok some science, since we're seeing a woeful lack of it! Ocatne is a fraction, distilled from crude oil. Oils are Hydrocarbons, and basically are named in order of how many carbon atoms are present Methane has 1, Ethane 2, Propane .blah blah until you get to Octane with 8 ad so on and so forth. Petrol doesn't actually contain much octane, but the RON is used a a guide to determine how the fuel compares with pure octane. (in easy to understand terms of course) 100 being equivalent to running on the pure stuff, although it concentrates solely on the anti knock properties of the fuel, and not necessarily on the energy released.

It should be remembered that the ignition timing should happen at the optimum moment and should be absolutely under the control of the engine management - working with a fuel that consistently delivers the right burn characteristics is important, and it's this which RON is aimed at. You don't want fuel that is is going to burn up early and wreck all your hard work in getting optimum burn which is why engines have knock sensors, which can adjust the timing if such conditions are detected. It does not automatically follow that higher RON = more ignition advance, since if you just keep advancing ignition you're actually forcing a pre ignition condition!

The fuel efficiency comes from the higher energy release from the fuel which is usually associated with the higher RON stuff, though as I've pointed out this is not necessarily the case since RON is not a measure of energy density, it's just 'usually' that's the case. The fuel amount used is controlled by a combination of different sensors, none of them the knock sensor, and most important being the lambda sensor. This on most cars gives only a binary output of lean or rich (vs the ideal theoretical perfect burn). By adjusting the amount of fuel entering the engine based on what the lambda sensor detects you can get a very efficient engine. Using a more energy dense fuel means you needs less of it to get the same burn, and the lambda sensor will consequently cause less fuel to be used when you use good fuel. Now the lambda sensor is normally ignored at wide open throttle so any gains this way are going to be very minimal if you are Larry Leadfoot, however, in such cases you are burning a predetermined amount of fuel which is the same no matter its quality, and should see a power increase due to the better fuel in such scenarios. I would love to see some actual figures attached to this for comparison but I'm not aware of any published data.

 

[nilagin]

Not surprised, race fuel is 104 octane upwards. You should see the flames out the TVR on that, but then that is ridiculously expensive.

Are ECU's mapped for both, or just run adaptives /wide band lambdas that cope?

I can't vouch for older engines, as I've only been in the job 4yrs, but the engines we are developing at the moment which will be replacing current engines which will be the same, the engines are developed on both fuels, if it is felt that more can be achieved from the engine and will be used in a semi high performance as opposed to a normal everyday engine then the engine will likely be mapped for the higher rated fuel. The knock control setting on the engine will retard the spark automatically if any knock occurs as a result of running on a lower grade of fuel.
If the knock level is set properly, then it is unlikely that any knock will be noticed whilst driving the car, the ecu is constantly altering the advancement or retardation of spark. One cylinder may knock more than others so some cylinders will burn fuel better than others, so whilst the spark may have been retarded for one cylinder it may produce the same spark for the next, if the knock control registers the spark could have been higher it will advance the spark for the next cylinder. This is why the engine will run smoother on a higher octane fuel as it won't need to keep retarding the spark so much and will be more stable.

Back to what the OP was asking about additives, as I said before, I only use Premium Fuel, Shell V-Power and that contains additives but as to whether it is better because of them I don't know. From what I have been told, Tesco 99 or Momentum what ever it is called now, achieves it's Octane rating by octane boosting additives, where as BP (97RON) and Shell (98RON) is the fuels actual rating without boosters.
I did however use BP Ultimate Diesel in my Mondeo like the petrol variant it does have additives to clean the engine. Because diesels can clog up the egr valve and inlet manifold with carbon, I would remove both items to clean them and there was barely a coating of carbon on them, yet I have seen pictures of egr valves and inlet manifolds that have been run on supermarket diesel and egr valves have been practically blocked with the build up of carbon and the inlet manifold had a coating of carbon several mm thick. So if premium diesel with it's cleaning additives works I have no reason to assume the cleaning additives in the petrol could be classed as snake oil.

Performance from different fuels.

View: https://www.youtube.com/watch?v=gQghB4asSnI

Cleaning

View: https://www.youtube.com/watch?v=nEdNCcdRIBI

 

[KMPhoto]

My anecdote [emoji3]:

From my reading of the topic over many years, there is a theoretical advantage to using premium diesel in new vehicles due to the extra lubricants added. How this plays out in real life situations is very difficult to quantify due to all sorts of factors, not least the way the engine is used.

I'm sure that if a proof were easily demonstrated, it would be freely available.

I always used premium diesel in both the Tiguan and Mondeo and along with oil changes at 8-10k miles, have had no problems.

My pal who runs a Passat on long life services (18k) and the cheapest diesel available has had no problems either.

 

[nilagin]

The fuel efficiency comes from the higher energy release from the fuel which is usually associated with the higher RON stuff, though as I've pointed out this is not necessarily the case since RON is not a measure of energy density, it's just 'usually' that's the case. The fuel amount used is controlled by a combination of different sensors, none of them the knock sensor, and most important being the lambda sensor. This on most cars gives only a binary output of lean or rich (vs the ideal theoretical perfect burn). By adjusting the amount of fuel entering the engine based on what the lambda sensor detects you can get a very efficient engine. Using a more energy dense fuel means you needs less of it to get the same burn, and the lambda sensor will consequently cause less fuel to be used when you use good fuel. Now the lambda sensor is normally ignored at wide open throttle so any gains this way are going to be very minimal if you are Larry Leadfoot, however, in such cases you are burning a predetermined amount of fuel which is the same no matter its quality, and should see a power increase due to the better fuel in such scenarios. I would love to see some actual figures attached to this for comparison but I'm not aware of any published data.

I do see the figures as it's part of my job, I'd love to share, but I value my job. I don't know if any of these figures would show up on a garage dyno computer. They must be able to register fuelling etc. as not all remaps are about power but economy also.

 

[ancient_mariner]

I generally use Tesco, Esso and Shell, and find little difference between them, even if using a premium version. However last week I filled up at Morrisons, being 6p/L cheaper than anyone else in the area, and I've noticed my fuel consumption has increased, at least for this tankful. Generally I'm skeptical, but just can't seem to get the same economy (I'd say 5% to 7% worse over a regular route).

 

[StewartR]

If your car drives in a manner that you are satisfied with why does it matter?

Because I would like to (1) save money and/or (2) prolong the life of my car, if either or both of these objectives can be achieved cost-effectively. So far I'm not seeing any evidence that they can.

 

[KMPhoto]

Because I would like to (1) save money and/or (2) prolong the life of my car, if either or both of these objectives can be achieved cost-effectively. So far I'm not seeing any evidence that they can.

Regular oil & filter changes are probably a better option for you given the age of the vehicle and the fact that premium fuel hasn't been used thus far.

 

[chrism_scotland]

I've personally not had a Petrol car, ever actually now I think about it, but I do tend to make a conscious decision to avoid supermarket diesel (more so now with the Mercedes), I certainly seem to get more miles out of Shell, BP or Esso fuel than my local ASDA or Morrisons.