Everything I've read suggested that the pump gas (10% ethanol) absorbs and holds much more water than does 100% gas. My 944 sits a lot and recently when I ran it, it was running as if only on 3 cylinders (I had parked it with less than 1/4 tank of pump gas). I ran numerous short trips and eventually, during each trip, it seemed to come back to full power. I found a station with 100% gas and filled with that. I have not had a single instance of the rough running since then. It is the gas? I don't know, but that is the only thing I changed.

 

Actually its the same price as 93 down here.

 

The ethanol seperated to gas and water or in the process of I think.

 

Shell V-power 91 octane is pure gas - no ethanol. The 93 octane you guys are running contains added ethanol in order to get the 93 rating. I used to use Sunoco 93, switched to Shell V-power 91 and I feel it runs just as well if not better.
I would prefer to run no ethanol at all if possible. As it states in our owner's manual, "You can use fuel with up to 10% ethanol, but switch back to pure gas as soon as possible."
As someone else mentioned, ethanol absorbs water and I live in a climate where there can be large temperature swings in the spring and fall, thus leading to condensation. I keep the tank topped up with real gas and have no problems.

 

FWIW rating systems in Europe are different from ours. 98 octane in Europe is the equivalent of our 93 octane here and 95 is our 91.