FLT CREW OF A320 EXPERIENCE FUEL LEAK ENROUTE. DIVERT TO NEARER SUITABLE ARPT FOR INSPECTION.

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DURING ROUTINE SCHEDULED ACR FLT TO ZZZ; IT WAS DISCOVERED AFTER 4 HRS OF FLT; THAT THERE MAY BE A FUEL LEAK IN THE R FUEL SYS. DEP WAS UNEVENTFUL EXCEPT FOR BEING HELD TO A LOWER CRUISE ALT INITIALLY FOR TFC. LOOKING AT FUEL USAGE AFTER THE FIRST HR; IT WAS NOTED THAT THE L FUEL TANK WAS OUT OF BAL BY 500 LBS LOWER THAN THE R TANK AND THE TOTAL BURN WAS 400 LBS OVER FLT PLAN BURN. FOR THE NEXT 2 HRS EVERYTHING WAS NORMAL WITH EACH HRLY CHK OF THE FUEL AND OTHER SYS. WHILE CONDUCTING HR #4 FUEL CHK IT WAS NOTICED THAT THERE WAS NOW A PROB WITH THE FUEL SYS; SPECIFICALLY THE R SIDE; 1000 LBS LESS THAN THE L SIDE. WHILE THERE WAS ENOUGH FUEL TO CONTINUE TO THE DEST WITH NO DELAY; 1500 LBS OF FUEL WAS UNACCOUNTED FOR. THE CAPT CONTACTED THE DISPATCHER VIA COMPANY RADIO AND IT WAS DECIDED TO DIVERT INTO ZZZ2; SINCE WE WERE 20 MI AND CLOSING AT THAT TIME. AN EMER WAS DECLARED WITH CTR AND THE CAPT RAN THE QRH FUEL LEAK PROC AND WE DIVERTED UNEVENTFULLY TO ZZZ2 COMPLYING WITH ALL COMPANY AND ACFT PROCS. THE FIRE CREW WAS STANDING BY ON THE GND AND DID A THOROUGH CHK OF THE ACFT ON THE RWY AND ESCORTED US TO THE GATE WHEN IT WAS DETERMINED SAFE TO DO SO. IT WAS DISCOVERED THAT THERE WAS A FUEL LEAK COMING FROM THE R ENG NACELLE. A MAINT LOGBOOK ENTRY WAS MADE AT THE GATE; PAX DEPLANED AND SWITCHED TO A NEW ACFT FOR THE TRIP TO ZZZ.