Conrad Allen It should last at least 30 minutes....

What is your answer?

Yes, and it may surprise many!

I may not want to find out  seeing I am flying in 8 days.

I don't know but I predict I will know soon.   

 Good morning Conrad. Long enough to get the plane to a safe altitude where we don't need oxygen. Probably 10 to 15 minutes.

Good morning Conrad. Hopefully long enough before the plane  lands.

Good for you for listening to the safety drill!  Most airline accidents occur on takeoff and landing when the plane is at a relatively slow speed and altitude, and the difference between getting out or not is knowing where the exit is and looking at the directions on getting the door open.  The crews get training to think about "what would I be doing right now if...."  and the answer is "Belt off!  Down the aisle!  Down the chute!  Run!"

Hopefully long enough ... at least until the plane crashes.

Oh YIKES, I don't know.  I will ask next time I fly...

I hope I never need to know this Conrad.

I don't know especially if someone is in a panic and hyperventilating.

Who knows Conrad, I hope long enough for the plane to land?

not long enough?

That's a good question and I have no idea how long. 

It depends how many are using the supply. You should be decending to below 10k feet. 10 to 15 minutes sounds right..

Never thought about that.  I hope there is enough time to land.

If those masks come down, you will have other problems to contend with

Wow, Ken Jones is the man with the best sounding answer!  I never thought about it, so I'd go with "hopefully long enough".

Hope I never have to find out.

30 min, or thereabouts?

No but hopefully long enough to get to alower level or land!

Well it doesn't matter, since by the time the O2 is depleted in the system, the plane will be at a low enough altitude to enable the stewardesses to roll down the windows.