If you want to take the time, follow a fuel tanker. I suspect you'll see it stop at Shell, Costco and Mom & Pop, not necessarily in that order.
Are you implying that Chevron gasoline does not contain their Techron additive? Is this whole "Top-Tier" thing really just a bunch of BS?
Did I just get lucky with my last car (ran perfectly at 140,000 miles without ever using any extra additive for injector cleaning, etc.)?
An interesting read:
http://www.caranddriver.com/features/05q3/your_car_is_a_temple_so_put_in_the_good_stuff.-column