TL;DR

You start with 45 seconds of oxygen. It depletes at 1 unit per second underwater.
Craft a Standard Air Tank to increase max oxygen from 45 to 75.
Upgrade to the High Capacity Air Tank to reach a maximum of 120 oxygen.
The Rebreather removes the depth penalty that drains your oxygen faster below 100 meters.
Air Bladders, Oxygen Tunics, powered bases, and vehicles all help replenish oxygen mid-dive.
The Oxygen Control Biomod reduces consumption when you’re stationary — very useful for scanning.

Oxygen is the first thing that kills you in Subnautica 2. You start with 45 seconds of air, which barely gets you through shallow dives let alone the deeper areas where the best resources and story content live. Getting your oxygen under control is the single most impactful early upgrade you can make.

This guide covers every method to replenish oxygen mid-dive and the full upgrade path from 45 seconds to 120 seconds of breathable air.

Table of Contents

How Oxygen Works in Subnautica 2

In Survival Mode, your oxygen depletes at 1 unit per second while you are underwater. Your default maximum is 45 units — that is 45 seconds before you start drowning. That drain rate does not stay constant, though. Once you pass 100 meters depth, the drain accelerates significantly. Below 200 meters, you can burn through your reserves in roughly 9 seconds without a Rebreather equipped.

Your oxygen meter only grows when you equip an Air Tank in your equipment slot. Tanks add on top of your base value rather than replacing it. If the HUD still shows 45 after crafting a tank, check that the tank is actually equipped in the paperdoll slot — not just sitting in your inventory.

In Creative Mode, oxygen is not a concern at all. Everything in this guide applies to Survival Mode only.

How to Replenish Oxygen Mid-Dive

Before worrying about increasing your maximum, you need reliable ways to top up while you’re already underwater. Here are all the methods available:

Swim to the Surface

The most basic method. Swimming to the surface restores oxygen automatically and quickly. It sounds obvious, but the challenge is making it back up in time when you’re deep. Learn to turn around earlier than you think you need to. If you’re pushing your luck, face upward when ascending — you move faster in the direction you’re facing, so swimming at an angle wastes precious seconds.

There is also a short grace period after your oxygen hits zero. Your vision blurs but you don’t actually die for roughly two seconds. If you’re close to the surface, don’t give up.

Oxygen Tunic Plants

Oxygen Tunics are blue stem plants found on the ocean floor in the early areas. They periodically release clusters of bright blue bubbles. Swimming through those bubbles replenishes your oxygen by +45 without needing to surface. This makes them extremely valuable during long dives.

Tag their locations as you explore so you can plan return routes through them. The caves near the Lifepod often have Oxygen Tunics, making early cave exploration survivable even with a low oxygen capacity.

Air Bladder

The Air Bladder is a craftable emergency tool. It has two uses: it instantly pulls you toward the surface when activated, and it can be consumed to replenish your oxygen by +25, giving you around 15 extra seconds underwater. It automatically refills its charge every time you surface or pass through Oxygen Tunic bubbles.

It is incredibly versatile. You can use it to escape from deep dives, dodge predators with a burst of upward speed, or simply buy yourself more time mid-scan. Carry multiple — they are cheap to make.

Air Bladder recipe: 2x Titanium + 1x Rubber. The blueprint is available by default. Rubber comes from processing 2x Lucifer Rotsacs at the Fabricator. See our guide on how to get Rubber from Lucifer Rotsacs.

Powered Base Rooms

Any powered base corridor or room with a hatch counts as a breathable air space. Entering it refills your oxygen to full, the same way the surface does. A single corridor with a hatch and a power source placed near a dive site is enough — it doesn’t need storage or crafting stations. Just drop it close to wherever you’re working and use it as a mid-dive oxygen station.

One important note: a base only restores oxygen while it has a working power source. If the power drops, the interior stops counting as a safe zone. Learn how to unlock the Habitat Builder and start building a base to set this up.

Vehicles

As long as your vehicle is powered, getting inside it restores oxygen and keeps it full while you’re piloting. The Tadpole — Subnautica 2’s first buildable submarine — provides unlimited oxygen whenever you’re seated inside it. This completely changes how long you can stay underwater. Check our full guide on how to build a Tadpole in Subnautica 2.

Portable Oxygen Generator

This is a mid-game device that you build via the Habitat Builder. It costs 3x Titanium and 2x Lithium to construct. It requires a Basic Battery to function and refills itself over time through electrolysis. When it has a full charge, using it gives you up to +15 oxygen. When it’s only partially recharged, you get as little as +5 oxygen.

The blueprint is found inside The Great Jaw location. Scan the device there to unlock the recipe. It is best used as a supplementary tool rather than a primary oxygen source.

Need Lithium? The Great Jaw area is also a decent Lithium farming spot once you’re ready to explore it.

How to Increase Maximum Oxygen in Subnautica 2

Replenishing oxygen is good. Raising the ceiling is better. There are two Air Tank upgrades that permanently increase your maximum oxygen capacity.

Standard Air Tank — Increases Max Oxygen to 75

The Standard Air Tank is the first and most important oxygen upgrade in the game. It increases your maximum from 45 to 75 oxygen, adding 30 extra seconds of dive time. The blueprint is available by default in your Fabricator — you don’t need to scan anything. You just need the materials.

Standard Air Tank recipe:

2x Titanium
2x Silver
1x Rubber

Silver is the hardest part. Head roughly 200 meters north of the Lifepod, just past the large Angel Comb plant. There is a cave entrance nearby with Silver nodes. Our guide on where to find Silver in Subnautica 2 will point you to the exact spots.

One important tip: do not spend your Silver on Wiring Kits or other electronics before crafting this tank. Oxygen capacity is the single most impactful early upgrade you can make. Everything else can wait.

Once crafted, open your inventory, go to your equipment paperdoll, and slot the tank into the designated tank slot. Your HUD will immediately update to show 75 as your new maximum. For Titanium, see how to get Titanium in Subnautica 2.

High Capacity Air Tank — Increases Max Oxygen to 120

The High Capacity Air Tank boosts your maximum oxygen to 120, adding another 45 seconds on top of the Standard Air Tank. This is a significant mid-game upgrade that makes long deep-water dives much more manageable.

This upgrade does not have a blueprint available at the Lifepod. You need to find a Recipe Data Card at the Research Center / Alien Ruins. Look for a datapad sitting on a crate in front of the entrance to unlock the blueprint.

High Capacity Air Tank recipe:

1x Standard Air Tank (consumed during crafting)
1x Plasteel Ingot

The Plasteel Ingot is made using the Processor at a cost of 2x Titanium and 1x Lithium. Read our guide on how to build a Processor and craft ingots if you haven’t set one up yet. Also make sure you know where to find other key resources as you progress.

How to Craft the Rebreather in Subnautica 2

The Rebreather does not increase your maximum oxygen. What it does is far more important for deep diving: it removes the depth penalty entirely. Without it, oxygen drains faster once you go below 100 meters, and the penalty compounds as you go deeper. Below 200 meters, you can lose your full oxygen reserve in about 9 seconds. With the Rebreather equipped, your oxygen ticks down at a flat 1 unit per second regardless of depth.

This makes the Rebreather essential for any serious mid-to-late game exploration.

Where to Find the Rebreather Blueprint

Head to the Colonist Bunker (Unauthorized NOA Modification), approximately 400 meters southwest of your Lifepod at around 88 meters below the surface. Inside, you’ll find an old Rebreather you can scan to unlock the blueprint. Scanning it once is all you need.

It can also be found inside the Cicada Wreck – Lander Garage to the northeast of the Lifepod, and in a wreckage area roughly 330 meters south-southeast of the Lifepod near the rocky pillars biome.

Rebreather Recipe

Materials:

2x Fiber Mesh
1x System Chip

Fiber Mesh is crafted at the Fabricator using 2x Fiber and 1x Strong Acid. Fiber comes from Fibrous Pulp — see our guide on how to get Fiber and Fibrous Pulp. Strong Acid is processed from Necrolei Cysts found around 300 meters north-northwest of the Lifepod. Full details in our guide on how to get Necrolei Cysts and Strong Acid.

The System Chip requires a Wiring Kit and 2x Quartz. The Wiring Kit needs Silver and Copper. See our guide on how to get Quartz and where to find Copper.

subnautica 2 biolab oxygen control biomod

Oxygen Control Biomod — The Underrated Passive Upgrade

The Oxygen Control Biomod is a passive Biomod that lowers your oxygen consumption while you are stationary. This makes it perfect for when you’re scanning objects, investigating structures, or waiting out aggressive creatures. You’re not burning air just standing still underwater.

To unlock it, head to the Welcome Center, roughly 85 meters southeast of the Lifepod. Insert a Basic Battery into the terminal near NOA to power the Biolab, then activate the Oxygen Control Biomod from the Biolab menu. It is one of the best early passive upgrades in the game and is easy to miss if you don’t explore the Welcome Center early.

You can also unlock movement Biomods at the same location, such as the Dash and Sea Skimmer, which help you travel faster and spend less time in the water between dives.

Movement Upgrades That Help Oxygen Management

Getting somewhere faster means spending less air on travel. These movement upgrades reduce the pressure on your oxygen without directly increasing your capacity:

Fins: Crafted at the Fabricator for a small but consistent speed boost. Easy to make early on.
Dash Biomod: Unlocked at the Welcome Center Biolab. Gives a burst-speed option for escaping danger or reaching the surface faster.
Sea Skimmer Biomod: Also from the Welcome Center Biolab. Improves surface movement efficiency.
Wakemaker: A mid-game crafted tool that significantly improves underwater maneuverability. Read our guide on how to make the Wakemaker for full details. Also check our guide on how to swim faster in Subnautica 2 for a full speed-focused breakdown.

Common Oxygen Mistakes to Avoid

Going deep before you have a plan. Open-water dives past 100 meters without the Rebreather or a nearby vehicle can turn lethal fast. Don’t push past that threshold until you’re prepared.
Spending Silver on electronics before crafting the Standard Air Tank. Silver is needed for the tank, and the tank is your most impactful early upgrade. Electronics can wait.
Entering large submerged structures on a half-empty tank. These spaces are disorienting. Always enter on a full tank and spend your first run locating any Oxygen Tunics or partially surfaced air pockets inside before going for scans and loot.
Panicking at zero oxygen. You have a two-second grace window after the meter hits zero. Stay calm, face upward, and keep swimming. If you do die, you can return and collect everything you dropped. See our guide on what happens when you die in Subnautica 2 so you know what to expect.
Ignoring Oxygen Tunics on the way out. Tag their locations going out so you can route your return through them on the way back.

Oxygen Upgrade Priority Order

If you’re not sure what to do first, follow this order:

Activate the Oxygen Control Biomod at the Welcome Center — free, fast, and immediately useful.
Craft Air Bladders — cheap and available from the start. Carry two or three at all times.
Gather Silver and craft the Standard Air Tank — this is your top priority before anything else.
Find and scan the Rebreather blueprint, then craft it before doing any dives past 100 meters.
Work toward the High Capacity Air Tank once you’ve reached the Research Center / Alien Ruins.
Build the Tadpole for unlimited oxygen on long exploration runs. See our full guide on how to build a Tadpole in Subnautica 2.

More Subnautica 2 Guides to Help You Survive

Subnautica 2 is available now in Early Access on Steam and Xbox, including Xbox Game Pass.

How to Increase Oxygen in Subnautica 2

How Oxygen Works in Subnautica 2