Oxygen Not Included

There are games that hold your hand, and then there are games that hand you a shovel and a science textbook before shoving you off a cliff. Klei Entertainment’s Oxygen Not Included falls squarely, and unapologetically, into the latter category. For years, Klei has cultivated a reputation for crafting unique, challenging experiences with a signature gothic-cartoon aesthetic, from Don’t Starve to Invisible, Inc. Here, they’ve applied their considerable talents to the space-colony simulation genre, and in doing so, have set its new high-water mark.

The premise is easy to state: guide a trio of 3D-printed colonists, or “Duplicants,” as they carve out a sustainable existence inside a hostile asteroid. The reality is anything but. This isn’t a game about painting idyllic colonies; it’s a game about fluid dynamics, gas pressures, electrical engineering, and metallurgy. Every single design choice, from the placement of a toilet to the angle of a pipe, has cascading, often catastrophic, consequences. The game doesn’t simulate survival; it simulates an entire ecosystem of physics and chemistry, one that is profoundly indifferent to the colonists’ continued existence. Other colony sims feel like pleasant sandboxes by comparison. ONI presents itself as a toy, but beneath the charming visuals beats the cold, hard heart of a university-level engineering simulator. It asks players not just to survive, but to understand. That demand for genuine comprehension is what makes it a significant intellectual achievement in interactive design.

• Deep Environmental Simulation: Every gram of material is tracked. Gases mix, separate based on weight, and condense. Liquids flow with realistic pressure. Heat radiates, transfers through materials, and will absolutely cook an entire colony if not properly managed.
• Intricate Base Engineering: The core of the game is designing and building systems. Not just rooms, but systems. Closed-loop oxygen recyclers, automated industrial kitchens, petroleum refineries, and eventually, steam-powered rocketry are all constructed piece by piece from a vast toolbox of components.
• Duplicant Management: The colonists aren’t faceless drones. Each has specific traits, skills, and, most importantly, stressors. A stressed-out Duplicant deciding to smash the colony’s only oxygen generator because the mess hall decor was “tacky” is a core, and strangely compelling, part of the design.

To call the opening stretch of Oxygen Not Included a “learning curve” is a disservice to the term. It is a sheer, vertical cliff face with very few handholds. First colonies are doomed to fail. Not maybe, not possibly. They will fail. The cause of death may vary—suffocation, starvation, heatstroke, disease, drowning in their own waste—but the outcome is certain. This is not a design flaw; it is the game’s brutal, brilliant onboarding process. Each failure is a lesson in physics. CO2 sinking is learned not because a tutorial says so, but because an unventilated farm suffocates. Heat transfer is learned because an unshielded water reservoir boils away.

The Engineering Imperative

Success in ONI is a function of applied science. The gameplay loop quickly evolves beyond basic survival into complex engineering challenges. The game doesn’t just hand over a machine that makes oxygen; it provides the tools to build an electrolyzer that cracks water into hydrogen and oxygen. What gets done with the heat and excess hydrogen it generates is the player’s problem. A problem that, if ignored, will become a catastrophic problem.

This is where the game reveals its genius. It forces thinking in terms of interlocking systems. That simple electrolyzer setup requires a dedicated, isolated power grid. Its heat output necessitates an active cooling loop, which in turn requires a source of cool liquid, a pump, and insulated pipes. This creates a cascade of design considerations that feels less like playing a game and more like managing a real-world industrial facility. The satisfaction of designing a truly self-sustaining, automated system is immense—an intellectual payoff few other titles can claim to offer.

Emergent Narrative Through Failure

The game has no scripted story, yet it is built to produce more compelling narratives than most AAA blockbusters. These stories are written by the player’s own triumphs and, more often, their failures. A breached pocket of super-pressurized chlorine gas can spawn a desperate, heroic attempt by a single Duplicant to seal the breach before succumbing to the fumes. A beautifully optimized colony, a marvel of engineering, can fall apart because long-term effects of metal refining on ambient temperature went unaccounted for. These aren’t cutscenes; they are the emergent, unscripted consequences of choices within a ruthlessly logical system. This is what makes Oxygen Not Included not just replayable, but endlessly memorable.

Klei’s signature 2D art style is on full display and serves the game brilliantly. The whimsical, almost rubbery look of the Duplicants and creatures provides a crucial visual counterpoint to the game’s punishing difficulty. It softens the blow when an entire population perishes in a tide of liquid metal. More importantly, the clean, readable graphics are essential for managing the game’s dense information. The various visual overlays, showing everything from temperature to gas concentration, are miracles of UI design, allowing complex problems to be diagnosed at a glance.

The simulation’s depth is also its primary technical liability. As a colony grows to dozens of Duplicants and encompasses massive, complex industrial chains, the number of calculations required makes this a demanding workload for any CPU. A 2D game of this scope is light on hardware early on, but sprawling late-game bases are built to strain processors—a significant crack in an otherwise masterfully polished product.

On Steam, this is a game built from the ground up for a mouse and keyboard. The interface is a dense web of menus, overlays, and tooltips. While expertly organized, it is fundamentally reliant on the precision of a mouse pointer for building, digging, and managing pipes and wires. Dragging out build orders, managing priority queues, and navigating the tech tree would be an exercise in frustration with a controller. This is a desktop-native experience, and the design decisions reflect a clear, correct focus on its primary platform.

Oxygen Not Included is not a game for everyone. Its refusal to compromise on its complexity is both its greatest strength and its most significant barrier to entry. This is a challenging, demanding, and at times, utterly infuriating experience. It is also one of the most rewarding, intelligent, and masterfully designed simulation games ever made, and we rate it among the very best in its category. Klei Entertainment has crafted a landmark title that will be studied by designers for years to come. For those with the patience to learn its unforgiving language, Oxygen Not Included offers a nearly bottomless well of intellectual satisfaction.