The below exerpt is from an article on slmarket.com
"During this morning stretch of relaxed 35 to 65 M.P.H. driving, the 600 turned in 231/2 M.P.G. Incredible for a 390hp, 6 liter, V12. Credit the automatic engine retardation (cams and electronics) on deceleration. Branson's street system is so poorly designed that we got our worst M.P.G. plodding through its NYC-type traffic: 151/2 M.P.G. Overall for 3,700 miles: 17.9 M.P.G. Do you know of any 6+ liter, gasoline powered car that can beat these numbers?"
This is one of the reasons I want it!