As is the case with any vehicle that moves through air, the faster you go, the more our atmosphere exponentially tries to slow you down and the harder the engine has to work to keep you at 80mph resulting poor FE. I would have to say that going that speed in a sub compact sardine can with other people in the car is a little outrageous...but that's only my opinion, no disrespect intended. A Benz S600 would be more appropriate/safer for the occasion.....