Flight crew of a B777-300 reported the received a 'fuel disagree' message on EICAS during cruise.

Attributes
ACN	1393963
Time
Date	201610
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Aircraft 1
Make Model Name	B777-300
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Indicating and Warning - Fuel System
Person 1
Function	First Officer Pilot Not Flying Relief Pilot
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Inflight Event / Encounter Fuel Issue

Narrative:

I was the first officer [not flying]. In the bunk sleeping at time of event. I was told of a suspected fuel leak and I returned to the cockpit. I observed an uneventful return to [departure airport]. Approximately two hours in to flight got 'fuel disagree' light on EICAS. Ran checklist. Fuel totalizer and calculated were 15;000 lbs different. Fuel log showed a discrepancy of plus 3000 lbs to minus 15;000 lbs in approximately 90 minutes. Suspected fuel leak. Turned around and proceeded to [departure airport]. Nearing [the destination] dumped to get down closer to landing weight while still leaving enough extra fuel in case of leak problem. Uneventful landing [another first officer] texted me after the flight and said maintenance found a faulty fuel processing card.

Original NASA ASRS Text

Title: Flight crew of a B777-300 reported the received a 'Fuel Disagree' message on EICAS during cruise.

Narrative: I was the First Officer [not flying]. In the bunk sleeping at time of event. I was told of a suspected fuel leak and I returned to the cockpit. I observed an uneventful return to [departure airport]. Approximately two hours in to flight got 'Fuel Disagree' light on EICAS. Ran checklist. Fuel totalizer and calculated were 15;000 lbs different. Fuel log showed a discrepancy of plus 3000 lbs to minus 15;000 lbs in approximately 90 minutes. Suspected fuel leak. Turned around and proceeded to [departure airport]. Nearing [the destination] dumped to get down closer to landing weight while still leaving enough extra fuel in case of leak problem. Uneventful landing [Another First officer] texted me after the flight and said Maintenance found a faulty fuel processing card.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.