Nearly every TV seems to get between 9 and 11 depending on speed and the shape of the trailer. In a careful test pulling from home to NJ and back (through OH/PA one direction, and DE/MD/WV/OH the other, towing at 60 mph, tailwind while going east, roughly equal headwind while going west), I averaged 11 mpg overall (12-13 going east, 9-10 going west). I get about 23 when not towing.
Before I bought this trailer, I towed a PUP and got around 17 mpg in this car (only towed the PUP with it a couple times before the new trailer arrived), and 15 mpg in the WindStar that preceded it.