Our cars are probably less efficient on average too, with all the SUVs. You've got miles/year and $/gallon, but not miles/gallon. You need all three to compare. I'd be interested in what you come up with.
For what it's worth, my commute is one mile and I drive a Mini, so I can't use the commute cost to justify my own salary...
US is quite easy to find; http://www.bts.gov/publications/national_transportation_stat... -> let's say 33 mpg for passenger cars (depends a bit on which vehicle classes you count). EU data is harder; Eurostat doesn't seem to track it (haven't searched very far - I'll ask my friends at the DG Transport if I don't forgot if they track it). http://www.greencarcongress.com/2004/11/average_fuel_co.html seems to suggest 43 mpg, but I don't see where they get their data from (the linked report is MIA). So US cars, in aggregate, use 30% more fuel. Which, intuitively, seems to be about right.
Taking into account gas prices, that still confirms that US citizens don't spend more than Europeans on gas, in absolute numbers, even given their different preference in cars, radically different urban development patterns and fuel purchasing power vis a vis the rest of the world.
For what it's worth, my commute is one mile and I drive a Mini, so I can't use the commute cost to justify my own salary...