Many drivers of cars that can run on regular gas actually buy premium in the belief that they will get better gas mileage. To test the belief. We use 10 card from a company fleet in which all the cars run on regular gas. Each car is filed first with either regular or premium gasoline, decided by a coin toss, and the mileage for that tankful is recorded. Then the mileage is corded again for the same cars for a tankful of the other kind of gasoline. We don't let the drivers know about the xperiment.

Regular

Premium

Differences:

1