Hello, this is my first post here. While I can't comment on Circle K gas in particular, I can tell you what I know from being a gasoline delivery driver. There are only four different loading facilities in my metro area of three million people. Two different refineries in the south metro, two loading facilities that are connected via underground pipeline from the actual refieries. I have only been to one of the refineries and one of the loading facilities. This means that with some weird exceptions I can't think of right now, every single gas station in my metro area is selling gas from one refinery or the other. I have only been carded in at one of the refineries and the associated loading facility on the other side of the metro. All the gas that's loaded out of that facility (let's use 87 octane for an example) comes from the same pipe. The only difference is the additives that each brand has and that might be maybe 20 gallons out of 4000 gallons of gas. Some are marketed to be cleaner for the environment and your car, some are marketed to make more power. In my personal opinion and that of everyone I've ever talked to about it, is that there is no real difference in gas between one brand and the next.
One big thing I wasn't aware of before I got the job delivering gas is the ratio of gas a normal gas station sells. They might sell 10,000 gallons of 87, for every 1500 of 89-90, and 1000 of 92-93. There are stations that might sell double the premium amount. The 87 gets rotated at busy stations every day. At the same busy stations it might take weeks to rotate the 92. A regular station might keep 16,000 87 oct, 5,000 89 oct, and 3,000 cot.
If the driver of the gas truck previously hauled E85 or diesel fuel and had a heel from the last delivery, it's possible that there's 25 gallons (more or less depending on the trailer and at how much of an angle the trailer was on when it was unloaded), of a fuel you don't really want in your tank. When you're talking about 8500 gallons of 87 going in one underground tank that will hold 20,000 gallons and they actually fill it to that, it's nothing. When you're talking about maybe 1100 gallons of premium in a tank that's kept maybe at 2000 gallons, it's a much bigger deal. Another issue is condensation.
Cliffs notes:
All gas is pretty much the same.
87 octane moves the fastest and is kept in the largest quantities, midgrade less so, and premium even less.
You're less likely to have problems with 87 octane fuel than 92.
The busier the station, the better.
This is all my opinion and I could be wrong on certain things.
