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". However, depending on the current depth, the player can deplete three or five units per second, so when the alert says "30 seconds", 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.
Extending Oxygen
The player's base oxygen capacity can be increased by 30 units by equipping a Standard Air Tank, which will give enough time for the 30 seconds alert to play. 120 units is the current maximum possible units of oxygen, which can be obtained through equipping the High Capacity Air 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 following tanks can be crafted to extend oxygen capacity:
- Standard Air Tank: +30 seconds
- High Capacity Air Tank: +75 seconds
- Ultra High Capacity Air Tank: +90 seconds (currently not available in survival)
The depth to which the player dives will initially affect the rate of oxygen consumption:
| Depth | Consumption Rate |
|---|---|
| Shallower than 100m | 1 unit per second |
| 100m to 200m | 3 units per second |
| Deeper than 200m | 5 units per second |
This depth penalty 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
- Interact with an oxygen-containing life form or environmental feature (see below)
- Enter a powered Seabase or vehicle
Oxygen is always present in the starting locations and the Lifepod. Oxygen will be automatically produced within a Seabase or Tadpole naturally, as long as they are powered with energy. If they run out of energy, no oxygen will be produced.
Environmental Oxygen
Oxygen Tunic
Oxygen Tunics are anchored lifeforms found in many biomes. The animal periodically produces bubbles of oxygen that float upward. If the bubble collides with the player, it will burst and be absorbed by the player, which refills the player's oxygen bar by 30 points and fills all Air Bladders.
Damaged Air Tanks
Throughout some Pioneer Seabases, some damaged Air Tanks can be found leaking O₂. They can be used to refill the player's Oxygen similar to the Oxygen Tunic.
Trivia
- 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.
- The player can last 7 minutes, 53 seconds underwater with a Rebreather, Oxygen Control biomod, and High Capacity Air Tank until the oxygen bar hits 0, with the death message displaying at 8 minutes, 8 seconds.
- During the intro segment in the wreckage of Sleep Bay 3, the player only consumes one unit of oxygen per second despite being hundreds of meters below the surface. This is likely a balance decision to prevent the intro from being too difficult.
