The owners manual says 91 octane. It really depends on how you drive the car. I know an old guy who has a C5 A4 and he puts 87 in with no knocking issues. The computer in the car will change the timing based on the octane of the fuel.
All the base gasoline is the same. What makes it different is the additive package. Those formulas are added when the fuel is pumped into the tanker for delivery.
The highest octane you can buy in California is 91.
If you are not getting 8 gallons per minute when you are at the pump, stop pumping, the filters are dirty and you could have problems.
Fill up at the coolest part of the morning because the fuel companies measure gas volume at 60 degrees. If you fill up a 20 gallon tank at 90 degrees, you are loosing .4 of a gallon. There is a lawsuit pending on this ripoff now.
http://www.cfnews13.com/News/Local/2...ed_debate.html
I generally use Chevron, BP and BJs wholesale on a rotating basis with no issues.
I filled up with BJs premium before a trip to Atlanta and averaged 29.0 mpg driving 75-90.