The XF 2.2D, which is powered by a 2.2-litre four-cylinder turbo diesel engine mated to an eight-speed automatic gearbox, recorded a figure of 4.49L/100km for a journey that took eight days and covered three time zones and 11 US states.
The Jaguar's official fuel consumption figure is 5.4L/100km, already an impressive number for a car that competes with the likes of the BMW 5-Series and Mercedes-Benz E-Class.
David and Alexander Madgwick, independent testers with economic driving experience, drove the standard-specification car at an average speed of 85km/h. They were accompanied on the trip by Jaguar's project manager for the XF, Paul Alcock.
The XF 2.2D went on sale recently in Australia, priced from $78,900.