From what I know of Newtonian Mechanics, if an object is moving at a constant velocity, the net force acting on that object is equal to zero. If there is friction, then the applied force required to maintain a constant velocity is equal to the magnitude of the force of friction, regardless of the actual value of the velocity.
Now let's suppose a car is driving on a road at a constant velocity of 10 km/h, and the force of friction acting on the car has a magnitude of 4,000 N. The applied force [from the engines] required to maintain the speed is also, therefore, 4,000 N[as the net force is equal to zero]. If the car travels on the same road at constant speed of 100 km/h, again, it would require the same amount of applied force from the engines to maintain the speed without acceleration: 4,000 N, as this "cancels out" the force of friction, and, per Newton's Second Law, the velocity does not change.
If moving at two different constant speeds–10 km/h and 100 km/h–on the same surface requires the same constant applied force generated from the engines, then why does moving at 100 km/h use up more gasoline?