If your G Class is just one of dozens of baubles in your personal collection--jumbled together with things like oil platforms and emirates--you probably don't give two shakes how many miles per gallon it earns on the EPA's highway cycle.
It's a good thing, because thinking about things like that could give you heartburn. In theory.
The carryover G Class, the 388-horsepower G550, is the only version with a semi-official fuel economy rating. Last year, the same model earned a staggeringly low EPA rating of 12 miles per gallon city, 15 miles per gallon highway. With no major mechanical changes, it's expected to be the same for the 2013 model year, though we'll update the information if it changes when the EPA sets it loose later this year.
That 12/15-mpg figure is the good news. The 544-horsepower, twin-turbo G63 AMG is likely to fare much more poorly on the gas-mileage tests, though standard stop/start technology could soften the blow on the G63 AMG's city-cycle economy.
The likely combined scores are the reason we've given the G Class a green score we typically reserve for supercars. It carries more than three times as many passengers as the average Lamborghini, but the G Class drinks gas just like an Italian exotic--or worse than one, depending on the model.