You guys are lucky, here in Brazil "half" the gas stations around sell a "mix" that have some gasoline, and God only knows what else along with it... Solvents, water, more ethanol than the regulation (~22% to 24%)... There has been this one time when I put gas V-Power (Shell branded gas station - noting against Shell itself) in my car, and the mileage dropped from 16km/l) to 11, checked in next refuelling. I've noted the bad performance right after leaving the gas station. :-(
Some gas station owners sometimes blend cheaper liquids (solvents or more ethanol) in the gas loads during its way from refinery to gas stations, and sell this piss as regular gasoline. The law enforcement and authorities monitoring is kinda poor and so us the car owners suffer from this plague.
Imagine that some time ago it was discovered gas station owners that managed, along with the pumps technician, to add an electronic device that, with a command from a remote control, tricked the pump indicator to sell a fuel quantity like 10 gallons - but showing 11 or 12 in the pump indicator ...
The bottom line is that one must try some gas stations and be a regular customer to that one(s) where your car behaves better...
