FUELING DISCREPANCY PARTIALLY CHALLENGED BY THE PIC OF AN A320 WHEN THE ARR FUEL THE PRECEDING EVENING DID NOT AGREE WITH THE PREFUELING AMOUNT ON THE FUEL SLIP AT PDX; OR.

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DURING COCKPIT PREFLT; THE FO DISCOVERED A FUELING DISCREPANCY CONCERNING THE 'BEFORE FUELING' QUANTITY RECORDED BY THE FUELER. THE FUEL SLIP SHOWED A BEGINNING QUANTITY OF 8700 LBS (4600 LBS L; AND 4100 LBS R) VERSUS ARR FUEL THE NIGHT BEFORE OF 10800 LBS (5100 LBS L AND 5700 LBS R). I ASKED THE FO TO CALL THE FUELER BACK TO DETERMINE THE CAUSE OF THE DISCREPANCY. (IT WAS ABOUT 15 MINS PRIOR TO DEP TIME.) I CALLED OUR OPS TO SEE IF THE APU MIGHT HAVE BEEN RUNNING ALL NIGHT; EXPLAINING THE 2000 LB DIFFERENCE. THEIR RESPONSE WAS 'NO.' (EXTERNAL PWR IS NORMALLY USED ON OVERNIGHT ACFT AND WE HAVE OUR OWN MAINT THERE.) THE RELEASE CALLED FOR A DEP FUEL OF 30000 LBS; AND THAT WAS EXACTLY WHAT OUR QUANTITY INDICATOR DISPLAYED. THE FUEL SLIP; HOWEVER; SHOWED THAT 2843 GALLONS WERE DELIVERED (DENSITY 6.79 LBS/GALLON) FOR A TOTAL OF 19300 LBS WHICH; WHEN ADDED TO A BEFORE FUELING LEVEL OF 8700 LBS; YIELDED A CALCULATED TOTAL FUEL ON BOARD OF 28000 LBS. A SEARCH OF THE LOGBOOK GOING BACK 2 MONTHS SHOWED NO FUEL QUANTITY SYS DISCREPANCIES; AND NONE WERE WRITTEN UP THE NIGHT BEFORE. THE FUELER ARRIVED WITH HIS SUPVR; BUT THE SUPVR WAS THE ONLY ONE THAT CAME TO THE COCKPIT. I EXPLAINED THE SIT TO THE SUPVR; AND ASKED IF IT COULD JUST BE A SIMPLE CASE OF 'MISREADING' THE BEGINNING QUANTITIES; ALSO POINTING OUT THAT THE APU HAD NOT BEEN RUNNING. THE SUPVR SAID THAT HIS FUELER STOOD BY HIS ORIGINAL RECORD. I EXPLAINED THAT IF THE APU HAD; IN FACT; BEEN RUNNING ALL NIGHT; THAT THE L TANK WOULD BE LOWER THAN THE R BECAUSE THAT WAS WHERE THE APU DREW ITS FUEL. THE SUPVR RESTATED HIS FUELER'S ORIGINAL POS; WHICH WAS BEGINNING TO RING A LITTLE 'HOLLOW;' COMING FROM A FACELESS IMAGE SOMEWHERE OUT OF SIGHT. IT WAS NOW SLIGHTLY PAST DEP TIME AND I; ULTIMATELY; HAD TO MAKE A DECISION WHETHER TO BELIEVE THE ACFT FUEL GAUGES (INSIDE AND WING PANEL BOTH AGREED) OR TAKE THE WORD OF THE FUELER. AFTER CONSIDERING THE FACT THAT THERE WAS NO HISTORY OF FUEL INDICATIONS; NO CURRENT SYS 'ABNORMAL;' A RPT FROM OUR OWN OPS PEOPLE THAT THE APU HAD NOT BEEN IN USE AND A 'GUT FEELING' THAT A 'FACELESS' FUELER WAS NOT BEING TOTALLY HONEST; I ELECTED TO DEPART WITHOUT TAKING A FURTHER DELAY TO HAVE THE TANKS' QUANTITIES MEASURED MECHANICALLY. THE FLT PROCEEDED UNEVENTFULLY TO MSP WITH NO INDICATIONS OF FUEL SYS OR WT AND BAL PROBS. IN RETROSPECT; I STILL FEEL THAT OUR FUEL QUANTITY INDICATIONS WERE ACCURATE; AND THE TIME IT TOOK TO BURN CTR TANK FUEL COUPLED WITH THE LACK OF ANY OTHER ECAM MESSAGES ENRTE (COMPUTER GROSS WT COMPARISON; ETC) REAFFIRM THAT. STILL; THERE WAS A STRONG 'PRESSURE' TO AVOID A MAJOR DELAY (THESE THINGS SEEM TO ALWAYS HAPPEN AT THE LAST MIN) AND IF THE SAME SIT WERE TO OCCUR AGAIN; I WOULD PROBABLY TAKE A DELAY TO HAVE THE FUEL TANKS 'STICKED.'