AN MD80 AT FL330 DISCOVERED CREW OXYGEN DROPPED TO ZERO. PREVIOUS HISTORY OF CREW OXYGEN PROBS. DIVERTED FOR OXYGEN SVC.

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DEPARTED ZZZ2 WITH COCKPIT OXYGEN PRESSURE LOWER THAN NORMAL; BUT XCHKED WITH FOM AND DETERMINED WE HAD MORE THAN THE MINIMUM REQUIRED PRESSURE FOR DISPATCH AT THE AMBIENT TEMP. DURING FLT AT FL330; I NOTICED MY MASK OXYGEN PRESSURE WAS ZERO AND IT DID NOT TEST. I ASKED THE FO TO CHK THE BOTTLE PRESSURE AND IT WAS ZERO. I REQUESTED A DSCNT FROM CTR AND TURNED THE ATC RADIOS OVER TO THE FO. THE FO FLEW AND TALKED TO ATC WHILE I ATTEMPTED TO COORDINATE WITH DISPATCH. THE ACARS ON THE ACFT WAS INOP; BUT I WAS ABLE TO TALK TO DISPATCH ON COMMERCIAL RADIO FOR A SHORT PERIOD. I DECIDED DIVERSION WAS THE APPROPRIATE COURSE OF ACTION BECAUSE WE STILL HAD 900 MI TO GO TO ZZZ1 AND IF WE EXPERIENCED SMOKE IN THE COCKPIT; WE WOULD HAVE NO OXYGEN TO BREATHE. BASED ON OUR POS; THE ONLY REALISTIC DIVERSION BASE WAS ZZZ. ZZZ4 AND ZZZ5 WERE TOO FAR AWAY AND OFF RTE. ZZZ6 WAS ON THE RTE; BUT WAS LESS LIKELY TO HAVE OXYGEN AND SVC THAN ZZZ. ALTHOUGH I DID NOT SPECIFICALLY REFER TO THE QRH; MISC 11; I PERFORMED EVERY ACTION REQUIRED BY THE PROC INCLUDING COORD WITH DISPATCH. WHILE DISPATCH WAS TRYING TO COORDINATE WITH ZZZ AND DETERMINE THE AVAILABILITY OF OXYGEN; WE LOST CONTACT WITH DISPATCH VIA COMMERCIAL RADIO. I COORDINATED WITH ZZZ CTR TO HAVE ANOTHER ACR X ACFT NOTIFY DISPATCH OF OUR INTENT TO DIVERT TO ZZZ. THE DIVERSION INTO ZZZ WAS UNEVENTFUL. KUDOS TO ACR Y GND PERSONNEL AND CONTRACT MAINT FOR DOING A GREAT JOB GETTING THE ACFT FIXED. DISPATCH AND MAINT ALSO DID A GREAT JOB. THE TRIP FROM ZZZ TO ZZZ1 WAS UNEVENTFUL AND THE OXYGEN PRESSURE SEEMED TO HOLD FINE. AFTER PARKING AT THE GATE; WE DID A CLOSE CHK OF THE OXYGEN PRESSURE AND DETERMINED WE HAD USED MORE THAN 300 LBS ON A 2 HR FLT WHILE WEARING THE MASKS FOR LESS THAN 5 MINS. I PUT AN INFO WRITE-UP IN THE LOGBOOK. SUPPLEMENTAL INFO FROM ACN 602016: UPON LNDG AND PARKING AT THE GATE; CREW OXYGEN BOTTLE PSI HAD DROPPED FROM APPROX 1700 PSI (DEP) TO 1400 PSI (GATE).