Yeah, that would be imperial gallons. We don't really measure stuff in gallons in the UK, its normally in litres; For some reason we don't calculate fuel consumption in Miles Per Litre though...
And yeah, i believe a UK mile is the same as a US mile.
I've often wondered why the US quote lower MPG figures than the UK, and now i know it's because of a difference in the measurement of a gallon! Thanks!