Subnautica 2: How to Replenish and Increase Max Oxygen

You start Subnautica 2 with 45 seconds of air. That sounds manageable until you find a wreck 80 meters down and realize you need to bail before you even finish scanning it. Oxygen management is the core loop of the early game, and the difference between a frustrating experience and a satisfying one comes down to knowing exactly which upgrades to chase and in what order. This guide covers every method to replenish oxygen on the fly, plus the full upgrade path from 45 seconds to 120 seconds of breathable air.

What does oxygen actually do in Subnautica 2?

In Survival Mode, your oxygen depletes at 1 unit per second while you are underwater. Your default maximum is 45 units, meaning 45 seconds before you start drowning. That rate does not stay constant, though. Once you pass 100 meters depth the drain accelerates significantly, and below 200 meters you can burn through your reserves in roughly 9 seconds. The Rebreather is what fixes that penalty entirely, but you need to earn it first.

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

Oxygen drains fast at depth

How to replenish oxygen quickly

Before you can increase your maximum, you need reliable ways to top up mid-dive. Here are all the methods confirmed across sources:

• Swimming to the surface restores oxygen automatically. Simple, but not always practical when you are hundreds of meters down.
• Your base (any corridor or room with a hatch) replenishes oxygen as long as it has power. A base without power does not help.
• Colonist Bunkers are abandoned habs you can enter for an oxygen refill. They also contain Biobed upgrades.
• The Tadpole vehicle restores oxygen while you are inside it. Park it near a structure entrance and use it as a mobile air station.
• Oxygen Tunic plants are bulbous teal plants with a purple tip that release breathable bubbles. Swim through those bubbles to refill. They also recharge your Air Bladder automatically.
• Air tanks left by other divers emit air bubbles you can swim through for a quick top-up.
• The Air Bladder (crafted from 2x Titanium and 1x Rubber) gives an instant oxygen boost when used. It provides +45 oxygen per use. Game Rant notes the figure as +25, so the exact value may vary by context or update. Assign it to a hotkey slot and use it when your meter gets critical. It refills when you surface or touch an Oxygen Tunic bubble.
• The Portable Oxygen Generator is a more advanced tool that runs on a Basic Battery and refills itself over time through electrolysis. If it is fully charged, you gain up to +15 oxygen per use. If it has only partially recharged, you get around +5. You carry it with you, making it useful for extended deep dives.

Air Tank upgrades: the full oxygen capacity table

Crafting Air Tanks is how you permanently increase your maximum oxygen. There are two tiers, and both are worth getting as fast as possible.

Both tanks are crafted at a Fabricator and equip automatically into your equipment slot. The High Capacity Air Tank consumes your existing Standard Air Tank as a material, so you do not need to craft a separate one.

Craft the Standard Air Tank first

How to craft the Standard Air Tank

The blueprint is available from the start. Head to the Fabricator in your Lifepod and look under the Personal/Equipment section. You need:

• 2x Titanium (common near the Lifepod)
• 2x Silver (the bottleneck)
• 1x Rubber (crafted from 2x Lucifer Rotsac, the glowing orange orbs in the starting biome)

Silver is the hard part. Head roughly 200 meters north of the Lifepod, just past the large Angel Comb plant. There is a cave entrance nearby with plenty of mineable Silver nodes. Game Rant similarly points players 150 to 200 meters north. Resist spending Silver on electronics until after you have built this tank.

How to craft the High Capacity Air Tank

This upgrade requires a blueprint you cannot unlock at the Lifepod. Swim from the Lifepod at a 210-degree compass bearing for roughly 300 meters. At around 80 meters depth you will find an underwater wreckage. Enter from the near side and grab the High Capacity Air Tank recipe data card from the table on your left. There is also a piece of Lithium on a table just outside the wreckage, which is exactly what you need for the recipe.

The recipe itself is 1x Standard Air Tank and 1x Plasteel Ingot. Plasteel Ingots are made in a Processor (2x Titanium and 1x Lithium). To craft a Processor, you need 2x Titanium, 1x Mild Acid, and 1x Copper Wire. You will also need your own base with a fully functional Fabricator, as the Lifepod Fabricator cannot craft the High Capacity Air Tank.

GameSpot's guide notes an alternative path: the High Capacity Air Tank blueprint can also be found at the Research Center or Alien Ruins, unlocked after completing objectives in the Tadpole Pens area. Both routes lead to the same upgrade.

How to craft and use the Rebreather

The Rebreather does not increase your maximum oxygen. What it does is remove the depth penalty entirely. Without it, your oxygen drains faster past 100 meters, and the penalty compounds as you go deeper. With it equipped, your oxygen ticks down at a flat 1 unit per second regardless of depth

To unlock the blueprint, head roughly 330 meters south-southeast of the Lifepod into the biome with the rocky pillars. Look for a wreckage area on the seabed. Inside a crate near the Dive Elevator, you can scan the Rebreather to unlock its recipe.

Once you have the blueprint, craft it from:

• 2x Fiber Mesh (made from 2x Fiber and 1x Strong Acid)
• 1x System Chip (made from 1x Wiring Kit and 2x Quartz)

Fiber is gathered from Fibrous Pulp using your Multitool on most organic matter. Strong Acid is processed from Necrolei Cysts, found around 300 meters north-northwest of the Lifepod. Wiring Kits require Silver, so you will need another Silver run if you have not stocked up.

For a deeper look at crafting the Rebreather step by step, the Subnautica 2 Rebreather location and recipe guide has the full breakdown.

Oxygen Control Biomod: the underrated passive upgrade

Before you have Air Tanks, the Oxygen Control Biomod is your best friend. Head to the Welcome Center, which sits around 85 meters south-east of the Lifepod, and insert a Basic Battery into the terminal near the NOA. This powers the Biolab inside. Activate the Oxygen Control Biomod there, and your oxygen consumption slows whenever you are stationary. Game Rant highlights this as especially useful while scanning, building, or sorting inventory underwater.

The Welcome Center also has the Dash and Sea Skimmer Biomods, which improve your movement speed. Moving faster means you reach Oxygen Tunics and surfaces more quickly, which indirectly reduces oxygen pressure on every dive.

Movement upgrades reduce oxygen pressure too

This is the thing most players overlook: oxygen management is not just about capacity. Getting somewhere faster means spending less air on travel. A few early movement options worth grabbing:

• Fins: crafted at the Fabricator for a small but consistent speed boost.
• Dash Biomod: unlocked at the Welcome Center Biolab.
• Sea Skimmer Biomod: also from the Welcome Center Biolab.
• Wakemaker: a later-game crafted item that improves underwater maneuverability, available from a fully functional Fabricator.

Common oxygen mistakes to avoid

After spending time in Subnautica 2's early areas, a few patterns cause unnecessary deaths:

Going deep before you have a plan. The caves near the Lifepod often have Oxygen Tunics, which makes them survivable even at low capacity. But open water dives past 100 meters without the Rebreather or a parked vehicle nearby can turn lethal fast.

Entering large structures without a full tank. Some submerged structures are disorienting. Enter them with maximum oxygen and spend your first run looking for any Oxygen Tunics or partially surfaced rooms inside before going for scans and loot.

Panicking when oxygen runs out. When you die from oxygen loss in Survival Mode, you respawn and can return to collect any dropped materials. The stakes are lower than they feel. Dying is annoying, not catastrophic.

Building a base for oxygen mid-exploration

Once you have the Habitat Builder, you can drop a simple powered room almost anywhere on the seabed and use it as an oxygen station. Attach a beacon so you can find it again. It does not need storage, crafting stations, or anything else. A single corridor with a hatch and a power source is enough to refill your air and let you push deeper.

For a full walkthrough on powering your base correctly, the Subnautica 2 oxygen and power base guide covers the Habitat Builder, power sources, and everything else you need to set one up properly.

For more survival systems across the whole game, the complete Subnautica 2 guides collection has you covered on everything from inventory expansion to advanced survival strategies.