MPG in usa gallon is a bit hard to quantify, on the canadian smart forums, 60-80 mpg is usual, some folks claim 113 mpg for optimum long distant highway driving, to 42 mpg for aggressive city driving when car was new. 56 mpg is combined estimate.

Which makes diesel a cheaper thing (< $300 cdn) if you decide drive from the pacific to the atlantic (4000 miles)

http://www.thesmart.ca/index.cfm?id=5058