I would think all of the gas is the same.
Although, Shell claims that their 93 Octane "V-Power"(some additive to clean gunk) is the best. But, their is no need for higher octane in a Nissan Sentra.
Im sure it is a myth.
Yes, it is slightly different...according to the commercials, Chevron with Techron has something extra special that cleans your engine as you drive.
When I've bought cars, though, none of them say "this brand gas will work for your car better than another..." and they all have federal requirements (as well as in some cases, state requirements) to meet, so I highly doubt there is a real, measurable difference in the performance of one gasoline brand over another.What are gas prices in your town?