Oxygen

Increasing
Putting a point into Oxygen will increase your maximum Oxygen by 20.

Breathing Time
A survivor starting with the minimum Oxygen value (100 Oxygen) can stay underwater for roughly 33 seconds before drowning occurs. Each point put into Oxygen increases the time you can stay underwater by roughly 7 seconds. Each second underwater costs roughly 3 Oxygen. For an estimate of how long your survivor can stay underwater, use this formula: Oxygen / 3 = time in seconds. For example, 300 Oxygen will provide approximately 100 seconds of underwater time: 300 / 3 = 100.

Swimming Speed
Points spent on Oxygen also improve your swimming speed by roughly 1.2%. All swimming speed bonuses (from Oxygen and Movement Speed) are multiplied by the 2.5x swim speed effect of SCUBA Flippers. Patch v256 lowered the swim speed gain by 80%. To configure the gain on a private server, you can change OxygenSwimSpeedStatMultiplier in the Server configuration.