B737-300 FLT CREW FLIES LOOP DEPARTURE AS FILED VICE OSHNN AS SHOWN IN THE REVISED ROUTE PORTION OF THEIR PDC CLRNC OUT OF LAX.

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WE WERE FLYING FROM LAX. WE RECEIVED OUR CLEARANCE VIA PDC. OUR DISPATCH RELEASE HAD US FLYING THE LOOP4 DEPARTURE. WE DID OUR PREFLIGHT CHECKLIST AND I VERIFIED THAT WE HAD THE LOOP4 AND ROUTE IN OUR FMC. THE TAXI OUT AND TAKEOFF WERE NORMAL. AS WE FLEW OUR DEPARTURE ATC CALLED US UP AND ASKED US WHAT DEPARTURE CLEARANCE WE HAD BEEN GIVEN. WE TOLD THEM OUR PDC HAD GIVEN US THE LOOP4. THEY INFORMED US THAT THIS EARLY IN THE DAY WE SHOULD BE ON THE OSHNN3 DEPARTURE. THEY GAVE US A VECTOR TO INTERCEPT THE OSHNN3 WHICH WE DID. I PULLED UP OUR ACARS RECEIVED MESSAGES TO LOOK AT OUR PDC. THE PDC HAD AN AMENDED DEPARTURE CLEARANCE FOR THE OSHNN3 WHICH SOMEHOW I DID NOT CATCH AS OUR PROPER DEPARTURE. SO WE FLEW THE WRONG DEPARTURE BECAUSE WE HAD NOT INTERPRETED THE AMENDED PDC CLEARANCE CORRECTLY. THERE WERE NO TRAFFIC CONFLICTS THAT I COULD SEE AND THE DEPARTURE CONTROLLER DID NOT SEEM TOO UPSET. THE REST OF THE FLIGHT WAS UNEVENTFUL. CHECK THE ROUTE AND THE PDC CLEARANCE AS PART OF YOUR CAPTAIN ROUTE VERIFICATION. HAVE DISPATCH FILE THE ROUTES ATC REALLY WANTS.