Driving with 3 passengers and a trunk full of stuff, and averaging 3.5 l/100km (67 mpg US) over 400km.
Next day I get
3.1 l/100km (76 mpg US) over 80km - no passengers or cargo, but with rear seats and no engine preheating.
Then the return: 4 passengers and even more cargo, plus a few small traffic jams, but still managed 3.6 l/100km (65 mpg US) over 350km. Then I drove the last passenger home and had the car to myself for the last 40km, so the engine was off more often than on, bringing the day's average down to 3.5, and bringing the coolant temps down too.
Upon returning home the fuel tank needle was on the halfway mark, over 1000km on the odo, and the onboard computer estimates another 880km until the next fill up. Of course, it'll be sooner than that, unless I drove like I drive the last 40km...