Not sure why all the hate when someone asks about gas mileage here. Nothing wrong with driving a performance car and wanting to reduce your carbon footprint or # of trips to the pump.
That being said, I am amazed at how efficient this beast is. I mean any car will drink gas if you flog it. e.g. famously see
But I usually get 20+ mpg on average with mixed driving when I am not on it all the time. This is amazing for a car with this much power. It even gets slightly better gas mileage than my previous F30 340 under comparable driving conditions.
Caveats apply of course (no 2 people have the same driving conditions/behavior/etc so take lots of salt with any mpg numbers ppl post)