Found this in a PDF file today. Pretty amazing if true, and I have no reason to doubt them.

Total Energy in a gallon of gas.

13% runs the car, consisting of 3% aerodynamic drag, 4% rolling resistance loss, and 6% braking resistance loss.

87% is wasted, consisting of 62% engine loss, 17% idling loss, 6% drivetrain loss, and 2% accessory loss.

See it in this PDF, on page 7:

http://www.ef.org/documents/2003AnnualReport.pdf