[mpg_numbers_guy]

Since you said miles per gallon, I'm assuming plug-in hybrids and electric cars do not count.

In that case the Gen 1 Honda Insight manual transmission would take the cake. It has one of the lowest drag-coefficients of any modern car, along with one of the most efficient engines. I have observed 70-80 MPG cruising at 65 MPH on the highway, if the wind isn't against me, in 40 F degree weather.

If you take into consideration plug-in hybrids and electric cars, then we're talking about miles per dollar, which is an entirely different scenario, since electricity costs are not directly related to gasoline costs in every area.