We have had our 2011 Quest for half a year and our real world fuel economy is in the following range:
Highway: 20.5 – 23.5 mpg
City: 16.2 – 19.6 mpg
If we travel on a flat highway at a steady speed we can get even better fuel economy but I would say the numbers above are pretty reasonable for the mountainous highways here in BC. I only use regular gas (not premium) and everything else on the van is stock. Current odometer reading is 13,000 Kms which is about 8,000 miles.