I don't think it is a universal truth that Shell premium gasoline is better than the rest. There are regional differences due to blending, for one thing. Also, there is more to consider than deposit control, although that is one thing to consider. I do like Shell's advertisements, especially the ones with Ferrari racing cars, but that doesn't sway my purchases. The issue with deposit control is that once you have sufficient and effective enough additives to prevent deposits building up on valves, there is no advantage to using more or better additives.

I tend to use Chevron gasoline due to their higher AKI (in my region), and their reduced use of ethanol. I can get 94 AKI with no ethanol, only at Chevron. That matters as much to me as deposit control additives. I use Shell when travelling. I also use Esso fairly regularly. All of those have essentially equivalent deposit control additives, and are name brand stations that tend to have good controls in place, reasonable quality control, and so on.

Full disclosure: I used to work with Chevron (in an independent distributor, not production); I have a family member working at Esso in distribution; and my former company used Shell as a supplier, rebranding their products to sell under our house brand. I know that they are all pretty much the same, even beyond the fact that they share bulk petroleum between them.

They sell 94 AKI in Canada? Cool.

Chevron exited the Southeast this summer, hence all their stations were rebranded. Whenever I can, I will buy no ethanol fuel regardless of brand name but that's not available in most locales. I prefer the idea of Shell and BP but I'm not willing to pay more than an extra 3 or 4 cents/gallon (about a penny a litre) for brand names. Exxon Mobil are not quite as easy to find in my area.

Only at Chevron AFAIK. Also, it may not be available across Canada, but it is available throughout BC. Another reason for you to go fully metric and move north.

In my area (Lower Mainland of BC) Chevron doesn't sell 91 for Supreme as they do in the rest of the province, they sell 92. Probably trying to use up all that 94 in the pump blend.

Chevron 94, or Supreme Plus, used to be quite a premium (pun intended) over Supreme, but lately it has been only $0.01 per litre. The frustration is we don't know if the 92 has ethanol or not. They have to have 5% across all their fuel sales, so it varies from time to time and from grade to grade. All pumps from 87 to 92 at Chevron are labelled "May contain up to 10% ethanol" but in reality they are likely half that.

None of this matters on the X3, which runs fine on 89, as did my X5, but the 535 notices the difference. And the X3 does run better with no ethanol, so that is enough reason to put 94 in it.

I am not sure how Canada is regulated, but in the US certain states mandate that 10% ethanol must be used in the gasoline (RBOBs). NJ, where I am from, is one of those states. Reality is, in the US at least, if the pump says "may contain 10% ethanol", it really does. The ethanol is added at the rack by calibrated equipment which is verified regularly. In addition, the stations are crosschecked for oxygenate (ethanol) content and octane all the time. In all my years, I haven't seen much less than 10% ethanol. Well, let me correct myself. There is 10% ethanol added at the rack but that ethanol is previously denatured with naphtha, thus you will not have the 10% ethanol based on purity, it is closer to 9.5% depending on denaturant and water content.
Your 535 notices the difference in putting downgraded fuel because it is turbocharged and the DME backs off timing because of the lower KI of fuel used. You wouldn't feel as much of the difference in x3, which has a naturally aspirated lower output engine.
I'm not trying to lecture you either, but I think it's good information for people who do not know and work is slow so I decided to go on a tangent.

For what it is worth, I was just told that Chevron and Shell purchase the best additive packages for diesel as well.

Interesting that you say that as here in Australia the "independents" as we call them are often as dodgy as hell. A few years back there was a big scam where what was sold as 91RON unleaded petrol actually contained up to 30%, or even 40% ethanol, the scam being the retailer could buy the ethanol virtually tax fee whereas petrol, regardless of the RON number, attracts a high government excise. Of course the "savings" by the fuel retailer where never passed on to the consumer. After there was a big spate of engine and fuel systems failures, and a subsequent investigation, both the state and the federal governments have moved to regulate the whole ethanol business.

Now the new scam is with diesel. The "independents" now buy dirt-cheap, tax-free bio-diesel, locally brewed from waste cooking oil, and mix it with refinery-delivered diesel. Again, the savings are not passed on to the consumer.

I personally know an Arco gas station owner who repeatedly purchased unbranded gas which he mixed in with the Arco supply. Needless to say he caused a few problems for his unwary customers. He got sued and can no longer own or operate a Gas station in California. I'm hoping Shell and Chevron do better job of monitoring their stations. It's a leap of faith but that's why I don't use the cheaper brands and unbranded gas/diesel.

As I noted in my post, the regulations here require 5% ethanol, but not by each pump, rather across all an oil company's fuel sales. So, you are likely to get closer to 10% on 87, offset by no ethanol on the 94 AKI.

I understand that my 535 is turbocharged. I assumed others did as well, so I didn't go into that.

I don't agree with the wording that 89 is downgraded fuel. An engine requires the lowest AKI possible that doesn't detonate. I have not found in my region (and different geographies are different) that my 325, Z4, X3, or X5 required 91 or 92. The best fuel economy I ever measured (tank to tank, not the OBC) was on 89 on more than one of these vehicles. The computer will not back off the timing if you put in a lower AKI fuel. It will back off the timing if it senses knock, whatever the AKI of the fuel is. If 89 doesn't cause knock, there is no retardation of the timing. The best indication of the timing being backed off (other than the rather inaccurate 'butt dyno') is to measure fuel economy. The fact that the X3, X5, and Z4 could get the same mileage on the 89 I bought locally indicates rather strongly that the timing was not being retarded.

The only reason that BMW specifies 91 AKI is because fuel quality (and AKI) follows a statistical bell curve in the real world, it isn't all what the label on the pump says. It varies so much in quality across North America that BMW specifies an AKI high enough that most owners won't have a problem with fuel so labelled. If you have crap fuel in your region, you may require 91 or even more. Conversely, if you have really good fuel, you may not need 91. My experience and testing on several vehicles bears that out. At the same time, I use 94 on the 535 because that engine can demonstrably take advantage of it.

I agree. I have German owner's manuals for the E90, F10, and F25. They make quite an important mention of fuel quality: minimal sulphur, nothing more than 10% Ethanol.

In all cases (except the N54), the absolute minimum is 91 RON. For the N54, the minimum is 95 RON.

In the E90 book, it recommends 98 RON for maximum advertised power. In the F25, it recommends 95 RON or higher. In the F10, there's no recommendation stated.

Doing the conversion, this translates to 93-94 AKI recommended for the E90/91, 91 AKI for the new X3, and no recommendation for the 5er. But remember that the fuel is much cleaner and better in Europe and especially Germany (I spoke with a German once who said US fuel as all kinds of "sh*t" in it). So use discretion.

BMW diesels are designed for diesel fuel complaince with DIN EN 590. This means a cetane of 51 or higher. Funny, because diesel with that high a cetane isn't even available around here, if at all.

All fair enough, but note that you can't actually do a true conversion. There are two different test protocols for the Research and Motor methods, and there is no direct mathematical conversion unless you know both R and M figures. In general, I use 5-6 points as a conversion, but different fuels will convert differently, due to their differing performance on the two different test engines involved.

That means that 95 RON is pretty much the same as 89, and 98 RON is pretty much the same as 92