Originally Posted by Razzy
Well not per say. If you compare Shell specifically they have their own additive but that too is a very miniscule amount. A fair comparison would be Arco's 91 to another "low end" gasoline brand.
With that said, there isn't as much difference between gasoline as people think (based on respective octane)
Would that miniscule amount justify the price enough for you to choose shell over arco ? Because where i live, difference between shell 91 and arco 91 is 30+ cents on average.