since (retirement) I watch the fuel gauge as much as the speedo
driving my Skoda Yeti, (4x4 with the 2 litre VW 140bhp Diesel engine), at around 100/110 kmh, (say 65 to 70 mph), on the Autoroute/Motorway/Freeway - I get 50 miles per Imperial, (UK) gallon, which would be 42 miles per US gallon, (an Imperial gallon is 1.2 US gallons, I believe) - which would be about 17 kms per litre
Driving at 130 kmh, (82 mph), the consumption drops to below 40 mpg - i.e. the car uses just over 20% more fuel - and to tell you the truth the drive is far less stressful and journey time are hardly any longer.
The Yeti is about as aerodynamic as a "house brick" so speeds about at 75 mph really do use up "the juice"