B777-222 INTL CREW ENCOUNTERS APPARENT FUEL LEAK. DIVERT TO NEAREST SUITABLE ARPT FOR INSPECTION AND MAINT.

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UPON ARR IN THE COCKPIT; WE WERE ADVISED BY THE RELIEF PLTS THAT THEY HAD RECEIVED A 'FUEL IMBAL' EICAS MESSAGE AND AFTER OBSERVING THE IMBAL HAD PROCEEDED TO PERFORM THE FUEL IMBAL AND HAD STARTED THE FUEL LEAK CHKLISTS (THE L MAIN FUEL PUMPS WERE NOW OFF AND THE L FUEL QUANTITY INDICATOR CONTINUED TO DECREASE AT A STEADY RATE -- APPROX 1000 LBS/MIN AND WERE NOW SHOWING A 10000 LB IMBAL. AFTER CONFERRING WITH MAINT AND DISPATCH; WE DECIDED TO DIVERT. WE RAN SEVERAL CHKS TO SEE IF WE COULD DIAGNOSE AN ACTUAL FUEL LEAK VERSUS AN INDICATOR ERROR. (WE WERE NOW INDICATING APPROX 40000 LBS IMBAL.) 1) WE OBSERVED NO YOKE DEFLECTION WITH THE AUTOPLT ENGAGED. 2) I CHKED FOR 'WING HEAVINESS' AND CTLABILITY WITH THE AUTOPLT OFF. 3) THE FO CHKED FOR VISUAL SIGNS OF LEAKAGE (NONE OBSERVED). 4) WE CHKED THE MAINT FUEL QUANTITY PAGE; WHICH SHOWED A POSSIBLE PROB WITH THE #1 SENSOR IN THE L MAIN TANK. WITH THESE OBSERVATIONS; WE COULD NOT CONFIRM AN ACTUAL FUEL LEAK. WHEN WE STARTED OUR DSCNT THE L FUEL QUANTITY INDICATION STARTED TO INCREASE STEADILY. BY THE TIME WE DSNDED THROUGH FL210; THE FUEL QUANTITY INDICATIONS WERE APPROX WERE APPROX EQUAL AT 50K A PIECE. WE DECIDED TO LAND OVERWT AND NOT TO DUMP FUEL IN THIS SITUATION. WE PERFORMED THE OVERWT LNDG CHKLIST. I PERFORMED A NORMAL APCH AND LNDG USING APCH SPDS ASSUMING NO FUEL LEAKAGE-THINKING CONSERVATIVELY.