What Steve says is true, Martin. Like Andrew says also, it depends on how you drive. It also depends on you're local area, where driving up hill and down dale may effect consumption too. The only way of getting guidance is to look at the Govt fuel figures and compare these against similar cars, like for like. Still not very accurate, but with so many variables there is little else to do. For the record, we get about 30mpg solo and 25mpg towing a twin axle, but here again the journeys are different, long motorway/dual carriageway trips when towing, town/fast A roads when solo.
The Sorento is a great car and at that price you can't loose.