How to increase O2 in Subnautica 2

Increasing your O2 capacity is one of the first things you’ll want to do in Subnautica 2. After all, it gets a bit annoying having to constantly resurface to gulp in air when you’re trying to accomplish basic tasks. Your overall oxygen level is the game’s real progression system, determining how deep you can dive and what rare resources are in your reach.

There are many different methods to boost your O2 and punch above your weight when under the sea, so here’s how to acquire and use each of them.

How to increase oxygen capacity in Subnautica 2

There are a number of ways to boost your oxygen, so here they are in order of when they’ll be useful to you and accessible:

Oxygen Tunics, Bloom Sap funnels, and air pockets

You can get O2 from Oxygen Tunics or by cutting Bloom Sap out of O2-filled funnels (Image credit: Unknown Worlds)

Your first port of call for breathing longer underwater is the Oxygen Tunic. Despite how it sounds, this isn’t a piece of gear, but is a blue blob-like organism that spits oxygen bubbles into the water. If you swim into these, you’ll refill your O2 as well as your Air Bladders.

While exploring, you’ll also find little funnels that are blocked by Bloom Sap. Hack this away with your Survival Multitool and it’ll produce a column of bubbles that you can hover in to slowly refill your oxygen.

Lastly, when you’re exploring caves, keep an eye out for air pockets in the ceiling you can dip into the refill oxygen. All of these are especially helpful early on when your oxygen capacity is low.

Oxygen Control Biomod

This passive Biomod slows O2 consumption when you’re still (Image credit: Unknown Worlds)

Once you’re able to craft a basic battery with an Acidic Raion Pouch (and have made a scanner), I recommend heading to the Welcome Center colony ruins just a short way to the southeast of the Life Pod. Here, you can plug a battery into a power outlet on the wall to use the Biolab, letting you slot Biomods (essentially skills) onto your character.

The Oxygen Control passive Biomod is absurdly good, lowering your O2 consumption when you’re still, making it perfect for when you’re scanning or investigating something underwater.

Air Bladders

Air Bladders are incredible for when you quickly need to rise to the surface (Image credit: Unknown Worlds)

These floatation tools are your best friend and I strongly suggest carrying multiple. You can craft one with:

2x titanium1x rubber

You can craft rubber with two Lucifer Rotsacs in the ‘Resources’ section of the Fabricator.

The reason Air Bladders are so good is that you can consume them to partially refill your oxygen, or use them to quickly rise to the surface when you’re running out of air. This makes them incredibly versatile and you can even escape predators with them since you rise so fast. Anytime you refill oxygen, you’ll also refill these little bad boys.

Standard Air Tank

Craft the Standard Air Tank as soon as possible when you start (Image credit: Unknown Worlds)

Your first proper oxygen expansion comes in the form of the Standard Air Tank. This requires:

2x titanium1x rubber2x silver

The silver is the trickiest part of this, but there are locations close to the Lifepod where you can easily grab it. Crafting this ups your overall O2 level, extending the duration you can stay underwater, so it’s a no-brainer to craft it as soon as possible.

High Capacity Air Tank

This is your next tank upgrade and getting it is a lot more involved. You’ll need:

To unlock the Sonic ResonatorTo build a base with a full FabricatorTo have the Standard Air Tank

You’ll have to acquire the High Capacity Air Tank recipe data card first, which you can find in a colony ruin in a deeper area to the southwest of the Life Pod—I’d suggest bringing Air Bladders and unlocking the Wavemaker so you can move quickly. The video above shows the route, but generally, you’ll want to:

Head southwest from the Life Pod over the drop-off in the ocean floor and skirt the wall to your right sideYou’ll pass a wreckage hanging over the edge and will spot a ruined colony structure straight ahead and below youHead inside to find the recipe on a desk

Make sure to also scan the Processor while you’re in here (you’ll need that in a sec), plus grab the Room recipe data card as well for your base. While you’re here, you’ll also need to collect some lithium, but luckily there’s one on the table just outside the colony ruins described above, resting in a piece of a coral dome.

Now all that’s done, you can head back and craft the High Capacity Air Tank. First, build the Processor (none of its components are hard to get) and then swap the recipe to Plasteel Ingot and chuck in:

2x titanium1x lithium

Combine that with your Standard Air Tank at the Fabricator and you’ve got your High Capacity Air Tank.

Rebreather

The Rebreather reduces oxygen loss when you’re diving deeper (Image credit: Unknown Worlds)

While the Rebreather doesn’t increase your oxygen capacity, it does reduce the O2 you use when diving deep. As I mentioned above, you can find and scan one of these in the habitation built into the cliff face, just north of those colony ruins where you find the High Capacity Air Tank recipe. All of this is to the southwest of the Life Pod.

To craft the Rebreather, you need:

1x System Chip2x Fiber Mesh

You can craft Fiber Mesh in the ‘Resources’ section of the Fabricator with two fiber and one Strong Acid, while the System Chip requires one Wiring Kit and two quartz, but you’ll already have the former unlocked since it uses silver.

Vehicles and Portable Oxygen Generator

You can scan a Portable Oxygen Generator inside The Great Jaw (Image credit: Unknown Worlds)

Though I haven’t fully unlocked this yet, you can find the first scan location for a Portable Oxygen Generator in The Great Jaw, close to the colony ruins where you found the High Capacity Oxygen Tank recipe and the lithium. It’s basically a giant pod-like mouth, so it’s hard to miss. Swim inside and scan the generator, though don’t trip the purple strands unless you want it to close.

Vehicles are another great way of maintaining oxygen, since as long as they’re powered, you’ll refill O2 whenever you get inside. You can build a Tadpole relatively early on using this linked guide, and it’ll be necessary for speedy and further exploration of the ocean.