Oxygen Not Included Walkthrough — Start to Endgame

Oxygen Not Included is Klei Entertainment's colony survival sim where you manage a group of Duplicants trapped inside a procedurally generated asteroid. Every breath of oxygen, calorie of food, and degree of temperature must be meticulously managed through complex piping, ventilation, and power systems. The Spaced Out! DLC adds multi-asteroid colonies and interplanetary rocket logistics. With hundreds of hours of depth in thermodynamics, gas physics, and liquid mechanics, ONI rewards systems-thinking players who enjoy solving cascading engineering puzzles.

This walkthrough takes you from your first session to endgame content. Each phase has specific goals, priorities, and milestones. Follow this path to avoid common traps that stall most players.

Quick Progression Summary

Phase 1: Getting Started — Starting Biome

The temperate starting area contains Oxylite for initial oxygen, Mealwood seeds for food, and Algae for early Oxygen Diffusers. Temperature stays around 25-30C, which is comfortable for Dupes. Prioritize securing water access and building basic infrastructure here before expanding.

Level/Difficulty: Cycles 1-50 Key Rewards: Oxylite, Mealwood Seeds, Algae, Sandstone, Copper Ore

What to Do in Starting Biome

1. Learn gas management. Gases in ONI have realistic density — oxygen sinks below hydrogen, carbon dioxide pools at the bottom, and chlorine settles above CO2. Spend your first session getting comfortable with this.
2. Pick Farmer as your starting build. It's the most forgiving option.
3. Build a SPOM (Self-Powered Oxygen Module) by cycle 30 — one Electrolyzer, two Gas Pumps, a Gas Filter, and a Hydrogen Generator in a sealed room provides oxygen for 8 Dupes with zero external power.
4. Acquire your first equipment upgrade — SPOM System or whatever's available.
5. Clear all main content before moving on.

Phase 1 Checklist

• Understand gas management fundamentals
• Farmer selected and functional
• Starting Biome main content cleared
• Ready for Caustic Biome

Phase 2: Early Game — Caustic Biome

A hot biome (40-50C) filled with Chlorine gas, Bleach Stone, and natural gas geysers. Chlorine kills germs, making it useful for sanitization rooms. The natural gas geysers here provide reliable fuel for Natural Gas Generators. Don't dig in without Atmo Suits.

Level/Difficulty: Cycles 30-80 Key Rewards: Natural Gas Geyser, Bleach Stone, Gold Amalgam, Fossil

What to Do in Caustic Biome

1. Work on pipe systems. Liquid and gas pipes form the circulatory system of your base, carrying water, polluted water, petroleum, and various gases. This system becomes critical from here on.
2. Farm for SPOM System if you haven't already. It's the key upgrade for this phase.
3. Insulate your base perimeter with Insulated Tiles made from Igneous Rock (not Sandstone) to prevent heat bleed from hot biomes — temperature creep is the silent colony killer.
4. Complete all objectives before pushing to Frozen Biome.
5. Consider whether Researcher might suit your playstyle better than Farmer.

Phase 2 Checklist

• pipe systems integrated into gameplay
• SPOM System acquired
• Caustic Biome fully cleared
• Ready for Frozen Biome

Phase 3: Mid Game — Frozen Biome

Sub-zero temperatures (-20 to -40C) with Wheezeworts, Ice, and Wolframite. This biome acts as a natural heat sink — smart players route hot pipes through it for free cooling. Wheezeworts provide 12kDTU/s of cooling without power. Rich in Wolframite for high-temperature-tolerant builds.

Level/Difficulty: Cycles 40-100 Key Rewards: Wheezeworts, Wolframite, Ice, Sleet Wheat Seeds

What to Do in Frozen Biome

1. Master duplicant skills. Each Duplicant has innate attributes (Athletics, Strength, Creativity, Science, etc. This unlocks a new layer of gameplay.
2. Start working toward Electrolyzer. It's the best equipment and becomes accessible around now.
3. Meal Lice into Liceloaf at a Microbe Musher is your safest early food chain: it requires no water, no cooking skill, and provides enough calories until you set up ranching or farming.
4. This area is the main skill check. If you can clear it, you're ready for late game.
5. Start investing in research tree for the tactical depth you'll need going forward.

Phase 3 Checklist

• duplicant skills mastered
• Electrolyzer acquired or in progress
• Frozen Biome fully cleared
• Ready for Oil Biome

Phase 4: Late Game — Oil Biome

The deep, hot biome (70-90C) containing Oil Reservoirs and Leaky Oil Fissures. Oil is refined into Petroleum for generators and Plastic for advanced buildings. This biome also contains Lead for radiation shielding. You need Atmo Suits and heat-resistant infrastructure to work here.

Level/Difficulty: Cycles 80-150 Key Rewards: Oil, Lead, Diamond, Abyssalite

What to Do in Oil Biome

1. Finalize your build. You should be running Researcher or Farmer with optimized gear.
2. Electrolyzer should be your primary. If you don't have it yet, prioritize getting it.
3. Never dig into Slime Biomes without Atmo Suits — Slimelung in polluted oxygen causes debuffs, and the Slime off-gasses polluted oxygen when exposed to regular atmosphere.
4. space exploration optimization starts here. Small improvements compound into massive advantages.
5. Farm this area for the resources needed to push into Space Surface.

Phase 4 Checklist

• Build fully optimized
• Electrolyzer upgraded to max
• Oil Biome fully cleared
• Ready for Space Surface

Phase 5: Endgame — Space Surface

The asteroid surface is a vacuum exposed to meteor showers and solar radiation. Build Bunker Tiles and Bunker Doors to protect solar panels and telescopes. Regolith from meteors must be cleared by Robo-Miners. This is where you launch rockets and harvest solar power.

Level/Difficulty: Cycles 150+ Key Rewards: Solar Power, Rocket Launch Pad, Space Research, Regolith

What to Do in Space Surface

1. Space Surface tests everything. Come prepared with your best build and gear.
2. Wheezeworts cool rooms by 12kDTU/s without power but consume Phosphorite as fertilizer. Place them in your farm or server room for passive cooling before you research Steam Turbines.
3. The endgame loop: run Space Surface, optimize gear, push harder content.
4. Experiment with Suit Wearer for a fresh take once you've mastered the standard builds.
5. This is where space exploration mastery separates good players from great ones.

Phase 5 Checklist

• Endgame content on farm
• Best-in-slot gear acquired
• Space Surface fully cleared
• Ready for challenge content

Common Progression Mistakes

• Printing too many Duplicants early — each Dupe adds 100g/s oxygen demand and 1000 kcal/cycle food demand, and colony death spirals start from overpopulation before infrastructure is ready.
• Ignoring temperature management until everything overheats — by cycle 100, heat from machines and hot biomes will cook your crops and stress your Dupes if you haven't built cooling loops.
• Building Electrolyzers without proper gas separation — unfiltered output mixes hydrogen into your oxygen supply, which Dupes can't breathe and which can cause hydrogen buildup in living quarters.
• Not insulating the base perimeter — hot biomes at 70C will slowly heat your 25C starting area through regular tiles, killing Mealwood farms that die above 30C.
• Running generators without Smart Battery automation — continuously running generators waste fuel and dump excess heat into your base, creating both resource drain and cooling problems.

Key Tips for Smooth Progression

1. Build a SPOM (Self-Powered Oxygen Module) by cycle 30 — one Electrolyzer, two Gas Pumps, a Gas Filter, and a Hydrogen Generator in a sealed room provides oxygen for 8 Dupes with zero external power.
2. Insulate your base perimeter with Insulated Tiles made from Igneous Rock (not Sandstone) to prevent heat bleed from hot biomes — temperature creep is the silent colony killer.
3. Meal Lice into Liceloaf at a Microbe Musher is your safest early food chain: it requires no water, no cooking skill, and provides enough calories until you set up ranching or farming.
4. Never dig into Slime Biomes without Atmo Suits — Slimelung in polluted oxygen causes debuffs, and the Slime off-gasses polluted oxygen when exposed to regular atmosphere.
5. Wheezeworts cool rooms by 12kDTU/s without power but consume Phosphorite as fertilizer. Place them in your farm or server room for passive cooling before you research Steam Turbines.

For detailed build optimization, see Oxygen Not Included builds. For quick wins, check tips & tricks.