ACR MLG VENTING FUEL ON TKOF AND CLB RETURNED TO DEP STATION FOR PRECAUTIONARY LNDG.

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FLT DEPARTED WITH NO DEFERRED OR OPEN ITEMS IN LOGBOOK. JUST AFTER ROTATION; TWR RPTED FUEL VENTING FROM RIGHT WING. MY INITIAL THOUGHT WAS THAT THE SURGE VENT TANK DUMPED ITS CONTENTS DURING ROTATION. I IMMEDIATELY WENT TANK TO ENG CONFIGN TO SEE IF ANY FUEL LOSS WAS NOTICEABLE ABOVE ENG BURN FIGURES. I SENT F/O BACK TO CHK AFTER ACFT REACHED 10000' MSL. HE RPTED BACK THAT HE COULD SEE NO FUEL VAPOR; BUT ADDED THAT A WOMAN PAX SAID THAT SHE SAW FUEL SPILLING DURING TAXI OUT. I ELECTED TO CONTINUE FLT SINCE THERE WAS NO EVIDENCE OF ANY FURTHER VENTING. JUST AFTER THE FLT LEFT FL180; ONE OF THE CABIN ATTENDANTS CALLED ON INTERPHONE AND RPTED FUEL COMING OUT OF THE WING AGAIN. I IMMEDIATELY REQUESTED AND WAS GRANTED CLRNC BACK TO THE DEP ARPT. INSPECTION AFTER BLOCKING IN REVEALED THAT FUEL HAD BEEN PORTING FROM A NORMALLY DRY AREA OF THE WING OUTBOARD OF THE SURGE TANK. DISCUSSIONS WITH MAINT IT CAME TO MY ATTN THAT THERE WAS AN ENTRY IN THE MAINT COMPUTER FOR AN INSPECTION TO BE PERFORMED ON THE NEXT LAYOVER TO DETERMINE THE SOURCE OF A POSSIBLE FUEL LEAK. THE COMPANY'S PROC OF KEEPING SOME ITEM IN LOGBOOK AND SOME IN COMPUTER LEAVES THE PIC IN A VERY TIGHT PLACE WHEN IT COMES TO THE TRUE AIRWORTHINESS OF THE ACFT.