Dallas seems to have the greatest delta in prices: yesterday at the Shell station:
87 octane: $2.20
93 octane: $2.90

Over $60 to fill the 2015 ML350, which I am still afraid to use regular in, what with direct injection and 12/1 compression. Of course the GM/Ford/japanese cars are getting more horsepower on similar engines using 87 octane.
Ya, you vill use der premium, and you vill like it!

DG