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From what I know, the base stock of all grades of gasoline is known as Alkylate. This is generally 74 octane and when produced is shipped to a large storage tank within the refinery. From there, when test come back it is within specs, it is sent to a blender to be finished into the final product for shipment.
The blending is done usually before shipping to stations. Blending is the adding of additives to increase the octane and adding of cleaners. The octane specs are approved by the feds as minimum.
Each refinery usually has a maximum radius they will ship to from their gates. More than this distance is not cost effective. For stations outside the radius, they are handled by what is known as spot market sales. As in my area, there are no refineries in my state and the closest is way too far to transport to. So we have spot markets supplying our stations. All refineries will sell their overage, some sell all product to this market. The system is like a major freeway system underground throughout the nation. They receive nothing but the base stock for further processing.
When a station orders a delivery, the suppliers, such as a Shell, Chevron, Mobil, Loves, Flying J and such will order the grade and if it is different than the normal blend, will specify the blend content. They blend to order and ship out to station.
As to the chemicals used for blending ... up till I retired 10 years ago, they were the same for all orders, just the percentage is different. But this is usually 1 to 2 percent different so it can be their propriety blend.
If there is another refineries close by, and many are, when one is doing what is called a turn-a-round of the unit and they can not make their base stock for their contracts, they pay the other refinery to supply until they are up and running again. My refinery was ARCO, and across the road was the Shell refinery (until they sold that refinery to another company). When they has the turn-a-round, I use to open the valves to ship the base stock to their refinery. So I have 1st hand knowledge of this.
And since we did not have a refinery in the Bay area, and Shell did, they took care of our needs. You wash my hand and I'll wash yours.
The main theme, all refineries met the minimum standards set by the industry and approved by the government, usually not exceeding, if at all, since the % profit would be effected.
What has happened since I retired is Shell advertising the additive of nitrogen (n2) to their fuel for better performance ? I tried to contact them to understand how an inert gas added to a volatile fuel will increases performance ?
They never responded, but I figured they wouldn't.
I can only assume that BMW recommends Shell fuel, like Cummins recommends Valvoline Blue Sync oil. They both will get something financial from it.
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