85+MPH MPG

42-44mpg
I have done a few NY-FL trips at that speed

 

but this is at 85, the faster you go the more it hurts. I pull about 50mpg at 65 47mpg at 70

 

In mid-April last year, I set my 2010 Prius cruise control at 80 mph going eastbound on a Ohio Superhighway( with a 70-75 mph PSL) - basically I filled the Prius up with gas and then drove it at 80 mph in the rain on a superhighway until I got the first beep and the last bar on the fuel gauge starte to blink - which at that point I drove into the most convenient gas station to get a fillup. The Prius MFD estimated its FE at 48 mpg but I calculated at the gas station that over 440 miles @80 mph that my Prius was getting about 44 mpg using 10% ethanol 87 octane regular gas. The driving temperature was about 65 degrees Fahrenheit and it was raining cats and dogs all day -- driving conditions were dismal. I was using Yokohama Avid s33d - iirc the tires were slightly over inflated at 38 psi front and 36 psi rear.