Increasing your O2 capacity is one of the most critical early-game priorities in Subnautica 2. Without adequate oxygen reserves, you are severely limited in how deep you can explore and which rare resources you can harvest. Managing your breath is not just about survival; it is the core progression mechanic that dictates your reach into the ocean's depths.
Fortunately, there are several methods to boost your oxygen management, ranging from environmental interactions to permanent upgrades. Here is a comprehensive guide on how to effectively manage and increase your oxygen levels underwater.
Early Game: Environmental O2 Sources
Before unlocking advanced gear, you must learn to utilize the environment. These methods are essential for extending your dive time without consuming resources.
Oxygen Tunics and Bloom Sap
Your first line of defense involves finding Oxygen Tunics. Despite their name, these are not wearable items but rather blue, blob-like organisms that release oxygen bubbles into the water. Swimming into these bubbles refills both your O2 bar and your Air Bladders.
Additionally, explore the environment for funnels blocked by Bloom Sap. Use your Survival Multitool to hack away the sap, revealing a column of bubbles. Hovering in these columns allows for a slow but steady refill of your oxygen reserves.
Air Pockets in Caves
When exploring underwater caves, keep a close eye on the ceilings. Air pockets often form in these enclosed spaces, providing a natural refuge. Dipping into these pockets allows you to refill your oxygen without returning to the surface, which is vital when you are caught in tight passages or pursued by predators.
Mid-Game: Permanent Upgrades
To truly expand your diving capabilities, you need to craft and install permanent upgrades. These tools significantly extend your time underwater and improve your safety.
Oxygen Control Biomod
Once you have crafted a basic battery using an Acidic Raion Pouch, head to the Welcome Center colony ruins located southeast of your Life Pod. Inside, you will find a Biolab. By plugging in your battery, you can access the Biolab to slot Biomods onto your character.
The Oxygen Control passive Biomod is highly recommended. It drastically slows your O2 consumption while you are stationary, making it perfect for scanning organisms or investigating ruins without fear of suffocation.
Air Bladders
Air Bladders are versatile flotation tools that serve as a safety net for emergency ascents. You can craft them using the Fabricator with the following materials:
- 2x Titanium
- 1x Rubber (crafted from 2x Lucifer Rotsacs in the Resources tab)
Consuming an Air Bladder partially refills your oxygen and propels you rapidly toward the surface. This makes them invaluable for escaping predators or avoiding drowning when your reserves run low.
Standard Air Tank
Your first permanent expansion of your O2 bar is the Standard Air Tank. Craft this as soon as possible to extend your underwater duration. The required materials are:
- 2x Titanium
- 1x Rubber
- 2x Silver
Silver can be found in locations close to the Lifepod, making this upgrade one of the first major milestones in your journey.
High Capacity Air Tank
For a significant boost to your oxygen reserves, you will need to craft the High Capacity Air Tank. This upgrade is more involved and requires specific prerequisites:
- Unlock the Sonic Resonator.
- Build a base equipped with a full Fabricator.
- Possess the Standard Air Tank.
Acquiring the Recipe
The recipe data card for this tank is located in a colony ruin southwest of the Life Pod. To reach it:
- Head southwest from the Life Pod over the ocean floor drop-off.
- Skirt the wall to your right, passing wreckage hanging over the edge.
- Enter the ruined colony structure ahead and below you.
- Find the recipe on a desk inside.
While here, scan the Processor and collect the Lithium found on a table outside the ruins, resting in a piece of coral dome. You will also need the Room recipe data card for base construction.
Crafting Process
Once you have the recipe, build a Processor and switch it to Plasteel Ingot mode. Combine the following:
- 2x Titanium
- 1x Lithium
Combine the resulting Plasteel Ingot with your Standard Air Tank at the Fabricator to create the High Capacity Air Tank.
Late Game: Advanced Oxygen Management
As you dive deeper, the pressure and oxygen consumption increase. Advanced gear is required to manage these conditions safely.
Rebreather
The Rebreather does not increase your total O2 capacity but significantly reduces the rate at which you lose oxygen while diving deep. This tool is essential for exploring the deeper biomes.
To craft the Rebreather, you need:
- 1x System Chip
- 2x Fiber Mesh
You can find the scan data for this item in a habitation structure built into the cliff face, just north of the colony ruins where you found the High Capacity Air Tank recipe.
Crafting Components:
- Fiber Mesh: Crafted in the Fabricator's Resources tab using 2x Fiber and 1x Strong Acid.
- System Chip: Requires 1x Wiring Kit and 2x Quartz. You likely already have the Wiring Kit unlocked via silver resources.
Portable Oxygen Generator
For extended missions, the Portable Oxygen Generator is a powerful tool. The first scan location can be found inside The Great Jaw, a massive, jaw-like structure near the colony ruins where you found the High Capacity Oxygen Tank recipe. Swimming inside this giant pod reveals the generator, offering a mobile source of oxygen for long-duration dives.
