The O2 Mask is initially acquired by Ratchet at Jowai Resort on Pokitaru, granted by the resort owner. The owner originally promised to give Ratchet the mask for escorting him to the other side of the resort, but he later promises to only give it to them if they can destroy the blarg's dump ships with the blargian starfighter. In subsequent games, the O2 Mask is initially available. The MegaCorp Helmet in Going Commando and Up Your Arsenal provides the same functionality as the O2 Mask.
In the original Ratchet & Clank, the gadget is not immediately available, and acquiring it makes a significant difference to the gameplay. It allows Ratchet to swim indefinitely and breathe in space, reaching new areas required to complete many missions. It also allows Ratchet to access some areas previously only available to Clank, such as Orxon and the outside of the Blarg Tactical Research Station. It also allows Ratchet to avoid damage from tanks firing toxic gas on Rilgar.
In other entries, the O2 Mask is initially available for free, and the player can automatically use it to breathe in space and underwater.
A redesigned, smaller O2 Mask fitting the face and mouth appears in the 2016 reboot. It is acquired in the same place on Pokitaru, though it is found in the pumping stations as an optional item rather than through the main path. The weapon also does not allow Ratchet to visit Clank's area in the Blarg Tactical Research Station, as th vis too small for him to fit through.
Ratchet wearing the O2 Mask
<Left> Ratchet, in space, with the O2 Mask <Right> Ratchet, breathing underwater, with the O2 Mas
Ratchet acquiring the O2 Mask (From the Resort Owner)