Petrol - are the brands all the same?

I don’t claim to know much about the different types of petrol but see that one major brand is claiming that by using their petrol your engine will become cleaner in 2 days. I thought that if I was purchasing unleaded it would have the same components regardless of which brand I used.


That’s a great question. I don’t own a car, but maybe @rimian, @consumerQld, or @frankcampagna have some insights.

I think the term “cleaner” would be open to interpretation. I remember a major car manufacturer claimed their car “cleaned the air” because its emissions were lower than some polluted environments the car may have been driven in.

My understanding is that petroleum does contain dissolved water and even can contain micro bacteria. So fuel quality could vary quite considerably depending on environmental factors.


I was told by a very well respected chemical engineer who works in the fuel refinery industry, that the basic fuel is all pretty much the same. The real differences are in what each company adds to the fuel at the end of the refining process, which includes cleaning agents that remove deposits that build up in the engine. This improves performance and economy. He recommended BP, Shell and Caltex fuels in that order.


That is true petrol formulations are usually the same with minor additions individualised by various oil companies to tailor their product and produce different octane ratings etc.
The issue of fuel that cleans engines goes back to the 50-60’s marketing, who can remember AMACO drives your engine clean?
Back then it was a common maintenance item of most car owners to have there engines periodically decoked due to build up of internal deposits mainly due older cooler running engines and inefficient combustion.
The necessity for a cleaning fuel died out during later years as tightening emissions and demands for improved fuel economy meant modern engine ran much hotter burned much cleaner and no longer required periodic decoking.

But alas the problem of dirty engines is re-emerging due to the adoption of new modern technologies such as direct injection petrol engines and common rail diesels with EGR, whilst the explanation of why it is re-emerging is quite valid, it is too long and boring for this forum suffice to say engine coking is re-emerging as a real issue and therefore a fuel that helps clean the engine is a now ‘again’ a worthwhile marketing strategy.


Using 98 octane is the cleanest and gives more km / litre. Worth it in the long run.

I have kept complete fuel economy records for years and am convinced that my cars run the same on any brand. They use a little more on E10 and I think it needs to be about 3 cents a litre cheaper because it has a lower energy rating. Other then that I have been running the cheapest available for decades with excellent results.


I find one of the irony’s of modern life is a lot people really concern themselves about fuel cost and chase around desperately to save a few cents a litre for their fuel and they may save possibly $2-4 a week, sometimes even less by looking for the cheapest fuel or using shopper dockets but they don’t bat an eyelid at the $$hundreds in value they shed every week in the loss of value and standing costs of their car.

And it really doesn’t matter what make or model is most cars shed upwards of at least hundred up to a few hundred dollars in value every week, depending on the depreciation from its original price, the financing & insurance costs etc.

And the double irony is some people happily shed that value and then chose to not drive very much in order to save petrol, so they bear that standing cost expense but don’t enjoy the benefits.

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Octane is a measure of the performance of a fuel in a moter of its ability to eliminate knock or preignition. To use it in a low compression moter is a waste of money. In a high compression moter it can turn a low performing moter into a good one, to the extent in some cares to change the speed that the gear box changes gears.

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98 provides slightly better economy in my 1.6L turbo than the 95 specified, but the incremental cost of the 98 over 95 is more cost than any saving from improved fuel economy. Using the lowest recommended octane is usually the smart choice. Of course 98 is advertised as having more detergents than 95 that has far more than 91, so it is not all just about economy.

Slightly off topic, but diesel…

I run a turbo diesel Mondeo and my mechanic advised to only use two companies (not sure if I can mention here) because when they refine the diesel they remove more and smaller grit particles. Meaning the engine gets less dirty, grinds/ wears out less, and the turbo has less change of damage.

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All fuel is refined to meet a specified standards of constituents including standards about max levels of contamination so I doubt there is much difference between what is supplied by the various oil companies. Remembering Australia currently only has two refineries left (and they may be shut soon) so pretty well all supplies must come from them or imported already refined. Fuel is only likely to pickup contamination during transport, storage and delivery handling. In most Australian cities it should be quite clean in remote areas there is a greater risk of contamination due to more transport handling and storage.
All Diesel engines use very fine fuel filters and water separators between the fuel tank and engine and it highly unlikely that serious contamination can ever get to the engine. It is likely that if a user was getting dirtier fuel this may require more frequent fuel filter changes, but manufacturers generally err on the side of caution with change intervals and assume the worst so filters generally have ample capacity to deal with any variation of purity in the supply chain.
But due to concerns about the risk of contamination to diesel fuel in remote locations many travellers, transport operators and farmers in these areas often add extra filters to the fuel system as a precaution.

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I do not have a diesel nor would my short distance driving make one attractive, but from interest in the topic, I found a good article on Practical Motoring “Is contaminated diesel fuel putting your engine at risk?”

We find Caltex is the only one that (almost) always has 95 octane fuel, which is what we use, so that’s where we go. A lot of the others seem to only have 91 or 98 (in this area, anyway) or even only 91. Whilst we could use 98 instead (and have done on occasion), we haven’t noticed any improvement in performance with the 98 vs 95, so the extra expense isn’t really warranted. So we’re not choosing based on “A’s 95 is better than B’s 95”, we’re choosing based on “A usually has 95 and B may not have it”…

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Surely it has more to do with how clean the fuel reservoir is underneath the bowser. If the individual petroleum station keeps everything clean, including changing filters. Everything will be okay.

Hi all, this article from @TonyIbrahim on dirty fuel might be of interest.

On interstate trips I always use 98 in my Territory. It goes a lot further and has overtaking power.
Stop - start City usage is a whole different cattle of fish, if you’re not too concerned about the cleanliness of your engine.

I feel that 95-98 octane is better for your car, so that carbon deposits do not slow you down if need to overtake etc.

The gearbox likes it too on ascends. No on/off, just smooth sailing.

A very interesting topic, as my car is a turbo, and also runs on diesel. I am never sure what is the best type of diesel for my vehicle, but would be interested to know. I do not mind paying more for a fuel that will give me better performance. Cheers, NatNat