I worked at Costco while in college many years ago and I got to see how the gas price was set for my specific warehouse.

Someone would drive out to a few neighboring gas stations, record prices, and set ours ~10 cents lower.

That’s it. That’s how the price was set.

Aside, working there was very good for a college job and I was treated very respectfully for the summers I was there.

I’m betting stores are given a floor price/cost and are given the flexibility to raise above that up to 10 cents cheaper than the nearest competitors in the specific area. All stores do not have the same ability/flexibility