Miles per gallon or gallons per mile?
A paper in Science entitled The MPG Illusion makes the case that the "miles per gallon" label is opaque and difficult for consumers to make calculations with. The authors have set up a one question online quiz to show how difficult it is to make judgments based on the miles per gallon label.
For details on the math behind it, check out this article from the USA Today. But it makes perfect sense: thinking about efficiency in terms of gallons per miles provides a clearer idea of fuel savings.
With all the emphasis on fuel efficiency, car makers and regulators could do a lot to make it easier for consumers to do research and make good decisions about transportation. The basic takeaway from the paper is this: seemingly small increases in fuel efficiency will save you a lot more gas than it intuitively seems like they would.