Originally Posted by Birdfan67

Working in the BMW/ auto industry for years it an ongoing argument . but for premium fuel 92 octane or better...Shell 31mg per 100ml - BP 26mg - Exxon 21Mg - Speedway 10.6mg- Mobile 10.6 mg- and down hill from there. Pilot worst of the bunch at 8.8mg... these are the measurements of detergents put in by the individual refineries ...as the gas is sold to these individual refineries often from same supplier, the government says all refineries must use a minimum amount of detergents and cleaners...some use more than others and even better quality...BP and Shell for all octanes 87-92 are the best.
Shell puts nitrogen mixtures and charges a little more for it...it mearly ignites more aggressively..is there a benefit for 8-10 cents more a gallon ??? maybe.

The biggest keys...use a pump that has multiple hoses , if you use a pump with a single hose...you could effectively pump 3-4 gallons of regular 87oct gas , when your paying for the premium. Not a good thing if your car requires premium grade.

Also visit a busy station...the fuel aren't in the tanks for weeks at a time...kind of like popping a beer and drinking it 4 hours later. Fuel can lose it's potency however still flammable.

Also Pilot, Citgo , Marathon are substandard with 10.6mg or less of detergents and cleaners per 100 ML , this is what ultimately helps your vehicle to perform better...not the octane measurement. Constant use of weaker fuels will lead to deposits and gum in injectors and lifters causing poor performance and reduced fuel economy .

Some Sunoco stores have up to 94 octane not necessarily better but...in the state of Delaware , they have less oxygen in the fuels and burn more efficiently...yielding slightly better overall performance and fuel economy.

Hope this helps !