One of the factors is how much bio-diesel is available. I hunted in Ireland five years ago and the vehicles were all diesel--but at that time they were running diesel almost entirely made out of Irish crops, thus no "bad" emissions.
A 4-door Mercedes passenger car did 50 mpg at 75-80 mph, and a full-size Toyota SUV did 35 mpg.
Yeah, the emissions deal is a problem, but bio-diesel is one of the reasons some offshore vehicles are so efficient. Of course, their fuel costs a lot more than gas and diesel here.
