As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE FLT, F/O USED O2 MASK, THE REGULATOR FOR F/O'S O2 FAILED. WENT TO 100 PERCENT 02 UNDER PRESSURE (EMERG) NOTE: USED 200 LBS OF O2 UNTIL TURNING OFF F/O REGULATOR. REMOVED AND REPLACED F/O'S O2 REGULATOR AND OPS AND LEAK CHECKED GOOD IAW DC9 MM 35-10-01-2-0001. RESERVICED CREW MAIN OXYGEN IAW DC9 MM 12-05-00-3 TO 1800 PSI.