In the B777-200, the center tank message is shown at approximately 14.5 gallons.
14 *decimal* 5. Does anyone else think the "138 gallons H20" thing is a missing decimal point? Otherwise the difference between the -200 and the -200ER is just shy a factor of 10; and I doubt the -200ER's centre tank is 10 times as big as the -200's.