Item that can create oxygen

[Vrock Bait]

Is their any item that can create breathable air? I would prefer to not generate a cyclone or anything with it(I’ve found a few items to generate tornados in Draconomicon). I need it so that a base for the PCs can’t just be invaded by the villain and they suddenly run out of oxygen, or the PCs find a clever way to dispel his plot device protections.

[DrMotives]

http://www.d20srd.org/srd/magicItems/wondrousItems.htm#bottleofAir This one ought to do it.

[Kalkra]

Or a Necklace of Adaptation.

[PoeticallyPsyco]

For a cheaper option, Stormwrack has these plant things that contain enough oxygen you can breathe through them even underwater. Something like 15gp and they last an hour?

[Darrin]

For a cheaper option, Stormwrack has these plant things that contain enough oxygen you can breathe through them even underwater. Something like 15gp and they last an hour?

Air plants last 5 minutes, but they're also weightless and thus don't count toward encumbrance. You could carry a bunch of them. I'm actually more partial to the Auran Mask (Complete Mage), which offers 10 minutes of air breathing, and also has negligible weight.

The Wind Pipe (Stormwrack p. 134) can also provide fresh air to an enclosed space for only 7000 GP.

[Venger]

periapt of the sullen sea (mic) also indirectly addresses this.