Jaguar's XK lineup, including the ultra-powerful, ultra-rare XKR and XKR-S, hit exotic-car performance heights with their V-8 engines. That performance doesn't come without a gas-mileage penalty, but the XK coupes and convertibles aren't as bad as they could be, thanks to lighter-weight aluminum body structures and six-speed transmissions.
For the 2011 model year, the EPA rated the base 385-horsepower Jaguar XK coupe at 16/24 mpg, its rear-drive chassis outfitted with a six-speed automatic. In convertible form, fuel economy falls a bit on the highway cycle, for an overall rating of 16/22 mpg.
Adding on a supercharger to the V-8 nets it 510 hp in the XKR hardtop and convertible--and gas mileage slips even more, to 15/22 mpg.
The EPA hasn't confirmed ratings for the 2012 model year, but they're not expected to change--though the XKR-S special edition could be rated separately.
Jaguar has recently announced plans to introduce hybrid technology to its lineup, but it's not likely to make it into today's XK, which is due for a replacement in the next two or three years.