Not all fuels sold at the pump are created equal. There are different fuels for different purposes, like aviation jet fuel, fuel for race cars, for agricultural use and for normal road cars. The latter can vary significantly.
Be wary of buying fuel with an unknown origin or brand. Worse still is to add your own additive, as this upsets the fine additive balance and might be very costly in the long run.
Click here for everything you need to know about what goes into your tank and ultimately your engine, courtesy of CAR Magazine.