AN A320 IN CRUISE RPTED LOSS OF #2 ENG OIL. ON GND DISCOVERED OIL CAP NOT SECURED.

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ON JUN/SAT/06; ACFT LANDED IN ZZZ FROM ZZZZ1. PER OUR COMPANY POLICY; A PREDEP CHK (WORK CARD) WAS ACCOMPLISHED. PER CHK REQUIRED OIL CHK AFTER 45 MINS TO WITHIN 2 HRS. OIL CHK ON #2 ENG WAS ACCOMPLISHED AND CHKED FULL. REMOVED OIL CAP AND PUSHED IN SCUPPER SEAL TO VERIFY FULL. REINSTALLED OIL CAP. SECURED CLOSED AND PULLED ON CHAIN TO VERIFY SECURED. CLOSED OIL SVC DOOR; OIL QUANTITY VERIFIED 22.4 QUARTS; MADE LOGBOOK ENTRY. #2 ENG WAS ON OIL WATCH. LOG ENTRY WAS MADE DURING CRUISE ON JUN/SAT/06. I FIND THIS INCIDENT IS INCONCEIVABLY WRONG. AS I FOLLOW THE SAME PROCESS FOR THE LAST 15 YRS; I WILL ALWAYS INSTALL OIL CAP AND MAKE SURE IT SECURED BY PULLING ON THE CHAIN WITH CONSIDERABLE FORCE TO MAKE SURE IT DOES NOT COME OFF. THEN I WILL DO A VISUAL CHK PRIOR TO CLOSING OIL SVCING DOOR. AS FOR MAKING SURE THIS WILL NEVER HAPPEN A SECOND TIME; I WILL FOLLOW THE SAME ACTION I HAVE PRACTICED FOR THE LAST SEVERAL YRS ALONG WITH ASKING A CO-WORKER TO HAVE A SECOND LOOK TO VERIFY CAP IS ON AND SECURED.