I have been tracking my MPG for 2 years now.

My 35d has returned a lifetime average of 29.7 MPG. That is a good cross section of roads, speeds and loads. Say about 10% country tracks, 25% town roads, 40% highway and 25% Motorway. Loads varied from one driver to 4 up with luggage and very occasionally pulling a small 6x4 trailer.

I am not light footed but I always keep my tyre pressures adjusted spot on for the load and temperature.

I'm in the UK (Imperial gallons) and I know American gallons are not full gallons but I don't think they are that much smaller.