Narrative:

During cruise flight, the captain left the flight deck to use the restroom. Upon the captain's entry to the flight deck, I noticed the oxygen level had dropped from slightly over 1500 psi before departure, to 1000 psi. A while later, we noticed the level had dropped to zero. We tested the masks and no oxygen flowed. We looked at the QRH and flight manual. No reference could be found to provide us guidance. We decided to contact dispatch and maintenance control. The decision was made to descend to 10000 ft MSL as soon as possible. We decided, in concert with maintenance and dispatch, to divert to ZZZ. The oxygen level was slightly above 1500 psi prior to departure from ZZZZ. Note: maintenance was unable to find a leak in the system in ZZZ.

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Original NASA ASRS Text

Title: A B737 FLT CREW NOTICED THAT THE OXYGEN BOTTLE LEVEL WAS DECREASING RESULTING IN A DIVERTED LNDG.

Narrative: DURING CRUISE FLT, THE CAPT LEFT THE FLT DECK TO USE THE RESTROOM. UPON THE CAPT'S ENTRY TO THE FLT DECK, I NOTICED THE OXYGEN LEVEL HAD DROPPED FROM SLIGHTLY OVER 1500 PSI BEFORE DEP, TO 1000 PSI. A WHILE LATER, WE NOTICED THE LEVEL HAD DROPPED TO ZERO. WE TESTED THE MASKS AND NO OXYGEN FLOWED. WE LOOKED AT THE QRH AND FLT MANUAL. NO REF COULD BE FOUND TO PROVIDE US GUIDANCE. WE DECIDED TO CONTACT DISPATCH AND MAINT CTL. THE DECISION WAS MADE TO DSND TO 10000 FT MSL AS SOON AS POSSIBLE. WE DECIDED, IN CONCERT WITH MAINT AND DISPATCH, TO DIVERT TO ZZZ. THE OXYGEN LEVEL WAS SLIGHTLY ABOVE 1500 PSI PRIOR TO DEP FROM ZZZZ. NOTE: MAINT WAS UNABLE TO FIND A LEAK IN THE SYS IN ZZZ.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.