I can't tell you with my 2010 Prius since I've never driven it over 65 mph but it was getting 56 mpg (no A/C) at that speed. My 1997 Volvo 960 2.9L, 24V, I6, 181HP, on the other hand is a fuel sucking pig. At 70 mpg she'll get 25.5 mpg. If I keep her at 65 mpg the MPG jumps to 28-29 mpg depending on the terrain and temperature.
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