According to a cars.com article the 2012 Wrangler will be getting a new 3.6L V-6 engine that will improve mileage about about 10%:
“The 2012 Jeep Wrangler will get a new 3.6-liter V-6 and a five-speed automatic transmission, mated to an all-wheel drivetrain. The update promises to improve gas mileage by 10%. The current Wrangler gets 15/19 mpg city/highway with an automatic transmission.”