We recently did a trip to WA and back, over 8,500 kilometres in 4 weeks.
On the way home we drove from Kalgoorlie to Ceduna without buying fuel in between, 1400 kms, used 259 litres of diesel so about 18.5 L/100. Gotta love the range with having 2 x 140 litre tanks, that was with a tail wind of...