Save some hard to find specialty fuels, most gasoline is a commodity product. Certainly the effectiveness of detergent additives make a difference in the long run, but there's nothing that should affect mileage or performance over one or two full tanks. In the same area, they're probably getting that fuel from the same depots and the same storage tanks, where the actual fuel could be coming from any number of different refineries, and possibly mixed. An individual refinery in turn may have differences in their fuel depending on the crude source.
About the only thing would be if it's improperly labeled (which can be considered fraud) or if the tanks are contaminated with water.
There's a term in the industry for this: a "branded commodity".
Quote:
http://blogs.platts.com/2010/08/23/unbranded_vs_br/
“All gasoline that comes out of refineries that has met governmental standards is then shipped via a pipeline where it is then put into a wholesale terminal of about 3 million gallons,” said John Eichberger, vice president of government relations at NACS.
From there the gasoline gets mixed with product from other refiners and then shipped through another pipeline to a storage facility.
At that point, said John Eichberger, vice president of government relations at NACS, there is no way to tell which gasoline was produced by which refiner.
“I don’t think retailers in the US can say with certainty where their fuel comes from,” said Lenard.
At Valero, spokesman Bill Day said that much is true.
“It is true in that gasoline is a fungible commodity,” said Day whose company owns and operates almost 1,000 branded stations in the US. “But there are certain detergent packages, added at the end, that make it brand specific. But it doesn’t necessarily mean that the gasoline that is for sale at a branded station was made by that refinery.”
Also - this was from 5 years ago before Valero decided that they'd participate in the Top Tier program:
Quote:
Valero’s Day said their gas stations do not offer a patented “value-added” detergent package to their gasoline.
“We have distribution agreements and add proper packages at the rack but we don’t have specifically branded additives,” said Day. “All of those packages add to price and Valero competes on price, not marketing.”
So Valero was one of the large refiners, but at the time they didn't have a chemical company make a specific additive for them, nor buy off the shelf additives that would be the only ones they used. They just used what generic additive was offered to them at the terminal, which is what a typical independent gas station would ask for.