Really bad MPG since winter hit??

[TerminatorX5]

the octane rating has nothing to do with energy packed in a liter/galon of fuel... all it is a retardant index that prevents the fuel from self-igniting under high pressure (sport engine, higher compression ratio, fuel self ignites before spark, piston knocks!!)... since that type of fuel is marketed to "sports" cars, that tend to be more expensive, the refineries sell it for more money (even though it is less "flammable") and also can afford adding more detergents and other additives, to make it more attractive to potential buyers...

Why the mileage has gone down in winter - i have no idea... mine has gone down a bit too, to about 16 MPG in a 2006 4.8iS, my driving is mostly highway but sometimes the highway is moving slower than city traffic... lol... I pull about 400 miles off a tank, give or take...