Date: 201906
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Workload; Distraction; Time Pressure
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Aircraft In Service At Gate
Result: General Maintenance Action
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: We arrived at the aircraft more than 40 minutes early for our flight. During the preparation of the aircraft for flight; I noticed in the logbook that the Crew oxygen system was serviced two days before. I noted that the Crew oxygen level was around 800 and mentioned it to the FO (First Officer). I then went into the AOM (Airplane Operations Manual) to check the minimum Crew oxygen requirement and noted that worse case for us would be 530 psi so we had ample to get to [our destination]. I showed the FO where this information was located in case he had to check it in the future. Shortly before we were scheduled to push; I was told we were going to be full and have some Jumpseat Riders due to a previous night flight cancellation. I got involved in checking ID's and making sure we would be good for weight. There were also some weather concerns [along the route]. We were finally wrapping up the boarding and two of the Jumpseaters came up and said they had to ride in the cockpit. I briefed them and got them seated as the weight and balance data came in. I did not think to check the minimum oxygen requirement for four people because I was in a rush to get pushed. When we landed; I told the FO to get Maintenance to service the oxygen and noted that the oxygen pressure was below 200 PSI. I wrote up the system and remembered the four people in the cockpit and that we had probably taken off with insufficient oxygen levels for four Cockpit Riders.I need to slow down and re-accomplish some of my checklist items again when the operations get rushed. Even though I had previously checked the Crew oxygen levels; changes occurred that put us out of limits.


Second narrative: During preflight we noted the oxygen quantity was around 800. While I continued my preflight duties; the Captain checked to see if the oxygen was legal for two Cockpit Crew; the altitude and duration of flight. We were legal with that quantity. We accomplished the Before Start Originating Checklist. Boarding was running pretty long; and very close to push time we found out we had two Jump seaters who had to ride up front. At the same time that was happening; a new ATIS came out with a runway change; and we reprogrammed and re-briefed the applicable changes. We were now a little past push time; we had a new student on an observation ride who we needed to make sure set the jump seat up correctly and who was inquisitive; we got the takeoff data and executed the Before Push Checklist and we both did not think to go back and relook at the quantity with four Cockpit Crew. By the time we arrived at the gate; the quantity had fallen to 200 though no one had been on oxygen.Just before push it gets busy; even without any additive factors. Slowing down for a second and just taking a breath might have allowed us to remember to look again at the oxygen level.


Synopsis: B737 flight crew did not verify oxygen quantity levels after addition of jump seat riders in cockpit.