Is there a difference in the quality of gasoline among different companies? I see Shell gas station sells premium unleaded (9/10) for 3:00/gallon, and across the street, Rotten Robie sells the same premium unleaded (9/10) for 2:60. I assume shell station might provide a better service (accepting almost all credit card, whereas in the Rotten Robie, you might have to pay by cash). But, for the automobile, is there a difference? Another one, Chevron advertise on a fuel additive called Techron. Do you see any difference in fuel efficiency if you use Chevron gasoline?