Date: 201905
Local time of day: 1201-1800
Location: ZZZZ.ARTCC, FO
Flight conditions: VMC
Aircraft: B767-400 and 400 ER
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Aircraft component: Oxygen System/Crew
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Time Pressure; Situational Awareness
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Landed in Emergency Condition; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: We were leveled at either FL300 or FL320; I cannot remember exactly which; and just about probably 50 to 80 NM east of ZZZZZ waypoint. My First Officer needed to use the rest room. He called the crew and within minutes; the Flight Attendant entered the cockpit and the First Officer stepped out.I was placing my mask on when I realized that something just didn't sound right. Specifically; when I first pulled the mask out of the stored position. There was no hissing sound or any flow of oxygen. I pulled up the oxygen page and realized that all cockpit crew oxygen was completely depleted. At that point; I did not want to alarm or panic the Flight Attendant that was currently in the cockpit.I waited for my First Officer to return and requested from ZZZZ Control to descend to FL250. I also requested that the Relief Pilot return to the flight deck. I got a hold of Dispatch to inform them of our situations and diversion options. At this point; I had already informed ZZZZ Control Sector that we were working on an issue with the aircraft. I told Dispatch that due to our current aircraft status; we couldn't continue and needed to divert. I mentioned I was looking at ZZZZ1 and ZZZZ2. The Dispatcher informed me that those two airports could only be used for emergency purposes only. I confirmed with dispatch that I would [be advising ATC]; at that point; we both agreed on ZZZZ1.I was very comfortable with ZZZZ1 because both myself and the First Officer had been there in the past and runways and facilities were adequate for our aircraft and passengers. Shortly after [advising ATC] we were asked to squawk 7700 by air traffic control. We were vector to a 15 to 20 mile final for Runway XXC. We relayed to ATC the souls on board of 248 and a total fuel on board of approximately 110;000 [pounds] of fuel. The landing waiting at touchdown was 397;000 pounds. The landing was were smooth and rollout was uneventful. Emergency personnel followed the aircraft to the remote stand. The emergency personnel inspected the landing gear we were given the all clear. I believe that from a CRM prospective; we all (flight crew; Dispatch; Maintenance; ATC; and emergency personnel) worked well together inside and outside the cockpit to get the aircraft safely on the ground.


Second narrative: During the preflight; I performed a full oxygen mask test by removing the mask; cleaning it; and then testing its operation by wearing it. Following the above; I finished the test by running oxygen through the mask for 10 seconds while observing the crew oxygen pressure in the Status page. Everything tested satisfactorily. Approaching intersection ZZZZZ at FL300 we started the process for a bathroom break. When the cabin was ready by the flight attendants; I transferred the controls to the Captain; and after letting a Flight Attendant in the flight deck; I went to the bathroom. When I returned; I noticed that the Captain wasn't wearing his mask. I sat on my seat and was informed by the Captain that the Crew Oxygen was down to 12 psi. The Captain transferred the controls back to me; requested a descent to FL250; and asked the Flight Attendant to coordinate the return of the Relief Pilot. While descending; I also took over the ATC communications while the Captain started communicating with Dispatch; [Maintenance Control]; and the Purser. After a short level off at FL250; we requested FL100 and [advised ATC]. We also agreed that ZZZZ1 was the best choice for a divert due to its proximity; runway length; weather; and emergency equipment/personnel availability. We were given vectors for an ILS XXC which was flown uneventfully. One of the challenges while configuring for landing was the min flap vrs max flap speeds that due to the weight of the airplane were very close to each other. The arrival was in smooth air so there were no flap over-speeds. We performed an overweight landing at 397480 lbs of which the ATC was informed. The touchdown was smooth with no side load and the deceleration slow so the brakes never heated up above normal. The emergency vehicles followed us to the remote stand and kept us informed of the wheel temps for approximately half hour after full stop; when they determined that there was no more threats related to hot brakes.We completed our crew debrief and discussed that we should have descended to FL100 quicker. Also; one of the flight attendants suggested to the Purser to send some portable oxygen bottles to us in the cockpit but he decided not to act on it not wanting to interrupt us during a busy time. We agreed that that would have been a good idea.


Synopsis: B767 pilot crew reported at cruise they discovered the crew oxygen system was empty.