1996 Oldsmobile Silhouette -This happened while I was taking a road trip and is all as highway mileage.
When I drive until the tank is near to empty I get 18-19 miles per gallon. When I fill up after going only a hundred or so miles I get more like 25-27 miles per gallon. I have checked my math and even had a friend check it. My road trip was several hundred miles long so I had an opportunity to test this a few times. Can anyone tell me how this can happen?