Oxygen

Oxygen (O2) is a gas that the player requires to stay alive during survival mode gameplay. When diving, the player uses a reserve of oxygen that diminishes over time. The HUD indicator for the player's oxygen supply is located on the bottom left of the screen, and the player has a base reserve of 45 units of oxygen. At first returning to the surface is the easiest way to find oxygen. This will quickly and automatically refill oxygen to capacity, however other methods can also be found to restore oxygen.
The PDA will initially alert the player if they have less than 10 units of oxygen remaining. The PDA will also alert the player when they have 30 units of oxygen remaining if they are diving far from the surface.The alerts play when there are 10 and 30 units left. The basic alert says "Oxygen", and with a capacity upgrade another alert says "30 seconds of Oxygen remaining". However, depending on the current depth, the player can deplete three or five units per second, so when the alert says "30 seconds of Oxygen remaining", there could be less than 10 seconds before the player asphyxiates. If the player runs out of oxygen, their screen will begin fading to black, and they will have about 4 seconds to get to an air source before the screen completely fades out, and another 4 before they die. In Hardcore Mode the player still needs oxygen to live, but all alerts will be disabled and will not make any sound alerts.
==Extending oxygen==
The player's base oxygen capacity can be increased by 30 units by equipping a Standard O2 Tank, which will give enough time for the 30 seconds alert to play. 225 units is the maximum possible units of oxygen, which can be obtained through equipping the Ultra High Capacity Tank. Air tanks will be automatically used when equipped, including being filled if in breathable atmosphere, and will keep their fill level if moved to the inventory.
The depth to which the player dives will initially affect the rate of oxygen consumption. When diving shallower than 100m of depth, the player will consume one unit per second; when diving between 100m and 200m, three units are consumed per second; when diving deeper than 200m, five units are consumed per second. This can be counteracted completely by equipping a Rebreather, which will cancel out all depth debuffs.
The player's oxygen reserve automatically replenishes whenever they:
* Rise up to the surface
* Swap an equipped empty O2 tank for a full one
* Eat a raw Bladderfish
* Interact with an oxygen-containing life form or or environmental feature (see below).
* Approach the end of a functioning Pipe
* Enter a powered Seabase or vehicle
Oxygen is always present in the starting locations, Lifepod 5 and the Drop Pod. Oxygen will be automatically produced within a Seabase, Seamoth, Seatruck, Prawn Suit, and Cyclops naturally, as long as they are powered with energy. If they run out of energy, no oxygen will be produced. If a fire starts in the Cyclops, it will produce smoke that causes the player to lose oxygen over time. Promptly put out the fire with a Fire Extinguisher to prevent suffocation.
==Environmental oxygen==
===Brain Coral===
Brain Corals in Subnautica release bubbles that rise to the surface, granting the player oxygen if they touch the bubble. Easily found even in the Safe Shallows biome and aboard peaceful Reefback Leviathans. They can also be planted in Exterior Growbeds at locations of the player's choosing for easy access.
===Ice Bubbles===
 
Ice Bubbles in Subnautica: Below Zero are a source of oxygen exclusive to the Arctic and underwater sections of the Glacial Basin. They require the player to cut them open through the use of a Laser Cutter, and when opened, will produce a steady stream of oxygen bubbles.
===Oxygen Plant===
Oxygen Plants in Subnautica: Below Zero are a flora species found in many deep biomes of Sector Zero. Interacting with the plant's bulb gives the player oxygen.
===Titan Holefish===
Titan Holefish in Subnautica: Below Zero are a fauna species found in the Sparse Arctic and the two Arctic Regions. They swim very slowly and are passive, but are surrounded by dangerous Symbiotes that will attack the player when approached. Interacting with the oxygen-filled ring inside their bodies grants the player oxygen.
== Trivia ==
* The player can use the console command oxygen to have unlimited oxygen.
* If the player is depleted of oxygen and gets to the surface when the screen is fading, the player will cough and sputter as opposed to just gasping.
* One of the unused game sound files, as well as a panel in Lifepod 5, states that the atmosphere also contains nitrogen, likely making it very Earth-like. It doesn't mention percentage contents, however.
*In early versions of the game originally it was shown that submarines would have had Oxygen. More or less oxygen would be in the submarine depending on the amount of space in the submarine. While for larger submarines this was removed in the 5th prototype, the Seamoth kept it's limited Oxygen until the game's Early Access release.
==References==
fr:Oxygène
ru:Кислород
Category:Mechanics