Mythbust supermarket petrol for me, please.

August 30, 2009 12:18 PM

Is supermarket petrol bad for my car?

It seems to be common knowledge that supermarket petrol from Tesco, Asda or what have you stations is inferior to the stuff from a "proper" petrol station. That it damages the engine in the long run for any of a variety of vague and poorly explained reasons.

Is there any substance to this idea, or is it just superstition? Googling gave me lots of conjecture but nothing authoritative.

UK-centric in case it matters. Thanks.

posted by Lorc to shopping (14 comments total)

Unless you're purchasing something like Shell Optimax (i.e. fuel with additives), it's identical.
Use away.
posted by knapah at 12:23 PM on August 30

It's cheap because they're using it as a loss leader to get people into their stores.
posted by knapah at 12:32 PM on August 30

From What Car?

Q: Is it true that the fuel sold at supermarket petrol stations is not of the same quality as that as you would buy from a dedicated petrol station?
Alex Wells

A: According to the Petrol Retailers Association, there is no difference between the standard petrol you buy from supermarkets or franchised petrol stations. In most cases the petrol and diesel is even produced at the same refinery and delivered in the same trucks.

The exception to this is specialist fuels, such as Shell’s Optimax and BP’s Ultimate. In their case, the fuel is enhanced with additives, which produce that brand’s particular properties.
posted by knapah at 12:32 PM on August 30 [2 favorites has favorites]

Supermarket pertrol is the same as anywhere else, short of the 'supreme psuedoscience version!' stuff you can choose to pay lots extra for at branded petrol stations. The reason it's so cheap is that it is a loss leader that gets people onto the supermarket forecourts, and then into the supermarket itself.
posted by Brother Dysk at 12:32 PM on August 30

In the US, it is from the same as gas station gasoline.
posted by tamitang at 12:39 PM on August 30

hmmmm. should have said "same refineries and is the same"
posted by tamitang at 12:40 PM on August 30

I worked for a fuel terminal company. This is how it works: Fuel is delivered in a very small number of pipelines. Terminals are the giant circular tanks that get their product directly from pipelines. If you're on the east coast, it's one of two pipelines. West coast, similar situation, different lines. The lines ship Premium, Regular, Diesel, and Jet fuel. Midgrade is a mixture Regular and Premium made at the time a tanker truck fills up at a terminal.

There are a handful of tanker truck operators in a given geographic area. Some consumer fuel providers, like Exxon, may have their own fleet of trucks. In any case, here's the important part. Every time a tanker truck driver (or the dispatcher) is tasked with obtaining fuel from a terminal, they select from the lowest price available among the local terminals. It's all the same fuel. They fill up the truck, and then deliver this fuel to the gas stations they service. The gas station owner does not care where the fuel came from.

Like in other businesses, there may be competitive agreements in place where, for instance, one tanker company gets a deal if they do business with one particular terminal. That has no effect at all on the fuel - remember - it's all the same fuel. If one terminal is out of Regular at the moment, the tanker drives to the next one and get Regular there.

What about additives? One particularly popular "special gas" sold by a particular company just contains two times the amount of the normal additive. This is keyed in by the tanker truck driver before he fills up the tanker at a terminal. Though the marketing for this particular product leads you to believe it's their own additive, it's not. It's the same as everybody else's, just twice as much.
posted by odinsdream at 12:42 PM on August 30 [7 favorites has favorites]

I see you're in the UK. I have no idea what goes on there. Sorry!
posted by odinsdream at 12:45 PM on August 30

Almost certainly exactly the same, given the global nature of fuel companies.
posted by knapah at 1:25 PM on August 30

Probably not exactly, if only for the simple reason that we don't have many independent petrol stations. So anything beyond the first paragraph of odinsdream's post doesn't apply.

It is still almost certainly the case that there are very, very few sources of petrol, and that they are used interchangeably by most or all of the big players (i.e. branded petrol stations and supermarkets) as they are identical product.
posted by Brother Dysk at 1:34 PM on August 30

For the most part, all fuel is going to be the same. The only time that you encounter a difference is the result of one gas station being busier than another. A busy gas station tends to have fresher gas since they run out faster and are refreshed more often. A station that sees less business has an increasing likelihood of having stale fuel.
Aside from that, the pump will have a sticker that indicates the percentage of ethanol added, if it makes a difference to you.
posted by Jon-o at 1:41 PM on August 30

Jon-o, read the OP's post properly.

There are no stickers indicating percentage of ethanol added on the pumps in the UK.
posted by Brother Dysk at 1:56 PM on August 30

I have gotten the impression that, in days of yore, there might have been differences in terms of how gas stations stored the fuel or maintained their tanks, so gas from Joe's Poorly-Run Station might have small amounts of suspended grit or emulsified water or dissolved crud. I don't think this has been a concern since, like, the 1950s or something, but it persists as a cultural memory, perhaps helped along by the occasional bits of FUD from marketing departments.
posted by hattifattener at 4:09 PM on August 30

hattifattener, part of it is probably also to do with improvements in engine tech - carburettors are much more prone to problems from impurities in fuel than are the modern filters that sit before direct-injection systems.
posted by Brother Dysk at 4:29 PM on August 30