A little more info on the story of 91 octane in California. The story you are about to hear is one I have heard from multiple sources (it was widely on the internet when this happened, but I don't see any evidence of it now.)
As most CA people probably remember, super used to be 92 octane. Then one summer the Unocal group (76, Phillips, Conoco) came up with a method to blend 92 octane fuel at a substantially lower cost than existing techniques employed by its competitors such as Chevron or Shell. This put Unocal at a substantial price advantage over its competitors, and Unocal offered to license this proprietary technique to its competitors for a fee. Rather than pay its competitor, Chevron, Shell, Valero, etc... basically did one over on Unocal by deciding to switch to marketing 91 octane instead (where no refiner had any cost advantage over the other). So literally overnight, super went from 92 to 91, and the cost to the customer did not change. Oil companies basically got to sell a cheaper product, for the same price, and Unocal got a big screw you from its competitors. Ironically, 76 stations kept 92 the longest, taking almost a month to completely switch over, suggesting this story may indeed be true. Sneaky huh?
I've heard other tales about how 92 octane was prohibitively expensive with the California Reformulated Gasoline formula, so 91 was used instead. But thats not nearly as interesting as the Unocal story.
Sorry if this is off topic, but I think most California folks would find it interesting.