The 87-91 is not a debate. The more alkylate in the fuel means more octane. The more more compression the higher the octane needed. Engines require just enough octane to prevent detonation. In other words, no need to spend extra money unless required. Higher octane fuels help with heat as well which goes up with compression. That said, most of the refineries in the basin are Co-Oped, meaning they all pump to shared tanks via companies like Kinder Morgan. As HotBoat said different additives are the only real difference, and it’s detergent. Commifornia has the strictest standards in the country. The fuel is all the same from all the refineries, or has to meet the same specs. Not to mention they sell blend stocks between each other. The Arco/BP/Tesoro-Andeavor/Marathon (haha) Carson refinery by itself was 25% of the western market and is now 33+% with the Tesoro Wilmington connection. It’s a shell game. Plus, I know its Arizona but next time you’re in Parker or the like, pay attention to the fuel delivery truck and watch it deliver to the Herbst Chevron, and then the non branded station up the road.