Oxygen (O₂) is a gas that is needed by the player to survive. When diving, the player uses a reserve of Oxygen that diminishes over time. If the player runs out of Oxygen, the player's screen will fade to black, and they will have only a few seconds to get to air before the screen completely fades out and they die.
The player's Oxygen reserve automatically replenishes whenever they come up to the surface, or enter a powered Seabase.
The HUD indicator for the player's Oxygen supply is located on the bottom left of the screen. The player has a base reserve of 45 units of Oxygen.
The depth to which the player dives affects the rate of Oxygen consumption. When diving less than 100m, 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.
- 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, different breathing responses will occur coming from the player.