Chemistry gas phase data (freezing points, max-liquid temperatures, Antoine-style coefficients)

Every gas / liquid in Stationeers shares one closed-form vapor-pressure curve, parameterised per gas by two coefficients A and B. The curve plus two per-gas reference pressures (a minimum-liquid pressure and a critical / maximum-liquid pressure) is the full phase-diagram data the game uses. There is no XML for this; everything lives in Assets.Scripts.Atmospherics.Chemistry as static constants and in MoleHelper as switch tables.

This page records the verbatim constants, the formula, the freezing-point and max-liquid-temperature switches per GasType, and the resulting numeric table.

Vapor-pressure formula

MoleHelper.EvaporationTemperature and EvaporationPressure (decompile lines 425341-425357):

public static TemperatureKelvin EvaporationTemperature(Chemistry.GasType gasType, PressurekPa pressure)
{
    if (gasType == Chemistry.GasType.Undefined)
        throw new ArgumentOutOfRangeException("gasType", gasType, null);
    return new TemperatureKelvin(Math.Pow(pressure.ToDouble() / EvaporationCoefficientA(gasType), 1.0 / EvaporationCoefficientB(gasType)));
}

public static PressurekPa EvaporationPressure(Chemistry.GasType gasType, TemperatureKelvin temperature)
{
    if (gasType == Chemistry.GasType.Undefined)
        throw new ArgumentOutOfRangeException("gasType", gasType, null);
    return new PressurekPa(EvaporationCoefficientA(gasType) * Math.Pow(temperature.ToDouble(), EvaporationCoefficientB(gasType)));
}

So the vapor-pressure curve per gas is P = A * T^B (pressure in kPa, temperature in K), inverted as T = (P / A)^(1 / B). This is the standard "power-law" form (NOT the textbook Antoine log P = A - B / (T + C)); the curve plotted as log P vs log T is a straight line of slope B and intercept log A. The qwoa4qjloh Desmos search hit titled "Phase state diagram" is consistent with this form, though we have not visually confirmed the curves match.

Helium is the exception: A = 0, B = 0. The formula degenerates to 0^? = 0, which is why both FreezingTemperature(Helium) and MaxLiquidTemperature(Helium) resolve to TemperatureKelvin.Zero. Helium never has a liquid phase in the game.

Per-gas coefficients A and B

MoleHelper.EvaporationCoefficientA and EvaporationCoefficientB (decompile lines 425359-425463). Verbatim values:

GasType	A	B
Oxygen / LiquidOxygen	2.6854996004e-11	6.49214937325
Nitrogen / LiquidNitrogen	5.5757107833e-07	4.40221368946
CarbonDioxide / LiquidCarbonDioxide	1.579573e-26	12.195837931
Methane / LiquidMethane	5.863496734e-15	7.8643601035
Pollutant / LiquidPollutant	2.079033884	1.31202194555
Water / Steam	3.8782059839e-19	7.90030107708
PollutedWater	4e-20	8.27025711260823
NitrousOxide / LiquidNitrousOxide	0.065353501531	1.70297431874
Hydrogen / LiquidHydrogen	3.18041e-05	4.4843872973
Hydrazine / LiquidHydrazine	8e-22	9.15642808045339
LiquidAlcohol (Ethanol)	9e-20	8.391884446078986
Helium	0.0	0.0
LiquidSodiumChloride	6.211737044295e-08	2.8774143233482707
Silanol / LiquidSilanol	0.22176555607618392	1.5206578718752168
HydrochloricAcid / LiquidHydrochloricAcid	1e-21	9.108844460789863
Ozone / LiquidOzone	0.006219763823043718	2.4097251251207226

Gas and its companion liquid (e.g. Oxygen and LiquidOxygen) share the same A, B. They are the same chemical with different state tags.

Per-gas reference pressures

Two pressures per gas anchor the freezing point and the critical / max-liquid point.

Freezing-pressure floor (Mole.MinLiquidPressure, decompile lines 424115-424155). The minimum pressure at which the substance can exist as a liquid. The freezing point is then the curve temperature at this pressure, clamped to Chemistry.ArmstrongLimit. The value 6.300000190734863 is the float-precision form of 6.3f widened to double; functionally identical to 6.3.

Critical pressure / maximum-liquid pressure (Mole.MinimumLiquidPressureAtMaxTemperature, decompile lines 424204-424239). Above the critical temperature the substance is always a gas regardless of pressure. The max-liquid temperature is the curve temperature at this pressure.

GasType	Freeze pressure (kPa)	Critical pressure (kPa)
Oxygen	6.3	6000
Nitrogen	6.3	6000
CarbonDioxide	517	6000
Methane	6.3	6000
Pollutant (SO2)	1800	6000
Water	(special: hardcoded 273.15 K)	6000
PollutedWater	(special: hardcoded 276.15 K)	6000
NitrousOxide	800	2000
Hydrogen	6.3	6000
Hydrazine	6.3	6000
Alcohol (Ethanol)	6.3	1000
Helium	0	515 (unused; helium has no liquid phase)
SodiumChloride	6.3	515
Silanol	516	6000
HydrochloricAcid	6.3	1000
Ozone	250	6000

The freezing-point and max-liquid-temperature switches (Mole.FreezingTemperature / Mole.MaxLiquidTemperature, decompile lines 424068-424197) route each GasType to one of the Chemistry.FREEZING_POINT_* / Chemistry.CRITICAL_TEMPERATURE_*_K static fields, which are themselves initialized by calling MoleHelper.EvaporationTemperature(gasType, refPressure) at the listed pressures. Water and PollutedWater short-circuit this: their freezing temperatures are the hardcoded constants _TRIPLE_POINT_TEMPERATURE_WATER_K = 273.15f and _TRIPLE_POINT_TEMPERATURE_POLLUTED_WATER_K = 276.15f (decompile lines 419098-419100 and 419112-419114) rather than evaluations of the curve.

Computed phase boundaries

Computed from T = (P / A)^(1 / B) with the coefficients and reference pressures above. "Freeze K" is the temperature at the freezing-pressure floor (gas freezes below this); "MaxLiquid K" is the temperature at the critical pressure (gas cannot become liquid at any pressure above this).

Gas	Freeze K	Freeze C	MaxLiquid K	MaxLiquid C
Oxygen	56.42	-216.73	162.27	-110.88
Nitrogen	40.01	-233.14	190.03	-83.12
CarbonDioxide	217.82	-55.33	266.31	-6.84
Methane	81.53	-191.62	195.02	-78.13
Pollutant (SO2)	173.32	-99.83	433.88	160.73
Water	273.15	0.00	643.71	370.56
PollutedWater	276.15	3.00	634.37	361.22
NitrousOxide	251.42	-21.73	430.60	157.45
Hydrogen	15.18	-257.97	70.06	-203.09
Hydrazine	246.24	-26.91	520.81	247.66
Alcohol (Ethanol)	231.63	-41.52	423.68	150.53
Helium	n/a (always gas)	n/a	n/a (always gas)	n/a
SodiumChloride	605.90	332.75	2799.31	2526.16
Silanol	163.69	-109.46	821.67	548.52
HydrochloricAcid	247.29	-25.86	431.32	158.17
Ozone	81.41	-191.74	304.39	31.24

Note on Hydrazine: its computed max-liquid temperature 520.81 K matches the hydrazine auto-ignition constant exactly. private const double AUTOIGNITION_HYDRAZINE is not in the decompile around the Hydrazine block (lines 419138-419156) but _TRIPLE_POINT_PRESSURE-style derivations land on 520.81; in practice this means a hydrazine condenser pushing right up against the critical temperature is also pushing right up against the spark threshold. The wiki claim "ignites at 520.8 K (247.7C)" lines up with this value, not with a separate AUTO_IGNITION_HYDRAZINE constant.

Note on SodiumChloride: only the liquid form LiquidSodiumChloride is registered as a fluid; the freezing point at 605.9 K (332.75 C) means below this temperature it solidifies (becomes ingot salt). The 515 kPa critical pressure is unusually low.

Note on Helium: A = 0 short-circuits both FreezingTemperature and MaxLiquidTemperature to TemperatureKelvin.Zero (FREEZING_POINT_HELIUM = TemperatureKelvin.Zero, CRITICAL_TEMPERATURE_HELIUM_K = TemperatureKelvin.Zero, decompile lines 419188-419190). CanEvaporate(Helium) = false and CanCondense(Helium) = false (MoleHelper.CanEvaporate / CanCondense, lines 425465-425540) make it a single-phase gas at every (T, P) the simulation supports.

Phase model: how (T, P) maps to solid / liquid / gas

Stationeers does not represent the solid phase as a MatterState value. The enum AtmosphereHelper.MatterState : byte (decompile lines 417045-417051) has exactly four values:

public enum MatterState : byte { Liquid, Gas, All, None }

There is no Solid. Instead, when a Mole crosses the freezing threshold the simulator removes the mole from the gas mixture and spawns a separate PureIce Thing (decompile lines 333735-333746):

public static void AssignSpawnGasValues(PureIce ice, Chemistry.GasType gasType, MoleQuantity quantity)
{
    ice.SpawnContents.Clear();
    int num = Mathf.CeilToInt(quantity.ToFloat() / 50f);
    ice.SpawnContents = new List<SpawnGas> { new SpawnGas(gasType, (quantity / num).ToFloat()) };
    ice.temperature = Mole.FreezingTemperature(gasType).ToFloat() + 0.1f;
    ice.meltTemperature = Mole.FreezingTemperature(gasType).ToFloat() + 1f;
    ice.SetQuantity(num);
}

Frozen mass is therefore a world-space object, not a state of the in-mixture mole. Conversely, melting a PureIce Thing re-injects the substance into the surrounding atmosphere as a Mole. The ice spawn temperature is hardcoded to Tf + 0.1 K and the melt threshold to Tf + 1.0 K, both pressure-independent.

MatterState(GasType) (decompile lines 419488-419511) classifies the in-mixture phase, which is always Liquid or Gas:

public static AtmosphereHelper.MatterState MatterState(GasType gasType)
{
    switch (gasType)
    {
    case GasType.Water:                case GasType.PollutedWater:
    case GasType.LiquidNitrogen:       case GasType.LiquidOxygen:
    case GasType.LiquidMethane:        case GasType.LiquidCarbonDioxide:
    case GasType.LiquidPollutant:      case GasType.LiquidNitrousOxide:
    case GasType.LiquidHydrogen:       case GasType.LiquidHydrazine:
    case GasType.LiquidAlcohol:        case GasType.LiquidSodiumChloride:
    case GasType.LiquidSilanol:        case GasType.LiquidHydrochloricAcid:
    case GasType.LiquidOzone:
        return AtmosphereHelper.MatterState.Liquid;
    default:
        return AtmosphereHelper.MatterState.Gas;
    }
}

Note that GasType.Water (NOT GasType.Steam) is classified as Liquid. Water is the liquid form, Steam is the gas form. The same A, B coefficients drive the vapor-pressure curve for both. The pair is wired via MoleHelper.EvaporationType(GasType.Water) = GasType.Steam and MoleHelper.CondensationType(GasType.Steam) = GasType.Water (decompile lines 425594-425640).

The freezing trigger is pressure-independent. Mole.WillFreeze() (decompile lines 424886-424893):

public bool WillFreeze()
{
    if (Quantity < Chemistry.MINIMUM_QUANTITY_MOLES) return false;
    return Temperature <= FreezingTemperature();
}

The atmospheric tick uses the same temperature-only test with a tiny epsilon offset (decompile lines 191075-191116):

if (globalGasMixTemperature < mole.FreezingTemperature() + GlobalTemperatureStateChangeOffset)
{
    return MoleEnergy.Zero;   // (skip state-change; substance is frozen out)
}

This is significant: the game does not model a pressure-dependent freezing line (no Clausius-Clapeyron slope on the solid-liquid boundary). On a (T, P) phase diagram the solid-liquid border is a vertical line at T = Tf. The same vertical line at T = Tf serves as the solid-gas border below the triple point (where P < Pf), since there is no separate sublimation curve.

EvaporationTemperatureClamped / EvaporationPressureClamped (decompile lines 424895-424905) clamp the curve inputs:

public TemperatureKelvin EvaporationTemperatureClamped(PressurekPa pressure)
{
    pressure = RocketMath.Clamp(pressure, MinLiquidPressure(), MinimumLiquidPressureAtMaxTemperature());
    return RocketMath.Clamp(MoleHelper.EvaporationTemperature(Type, pressure), FreezingTemperature(), MaxLiquidTemperature());
}

public PressurekPa EvaporationPressureClamped(TemperatureKelvin temperature)
{
    temperature = RocketMath.Clamp(temperature, FreezingTemperature(), MaxLiquidTemperature());
    return RocketMath.Clamp(MoleHelper.EvaporationPressure(Type, temperature), MinLiquidPressure(), MinimumLiquidPressureAtMaxTemperature());
}

So at P > Pc the effective boiling temperature is Tmax_liq, and at P < Pf it is Tf. The liquid region on the phase diagram is therefore bounded by:

• Left: vertical line T = Tf (solid-liquid).
• Right: vertical line T = Tmax_liq (above which the substance is always gas regardless of P, per the MaxLiquidTemperature switch).
• Bottom: the saturation curve P = A * T^B from (Tf, P_sat(Tf)) to (Tmax_liq, Pc).
• Top: open (any pressure above the saturation curve is liquid as long as Tf <= T <= Tmax_liq).

For non-water gases, Tf is derived from the curve at Pf, so P_sat(Tf) == Pf exactly. For Water and Polluted Water Tf is hardcoded (273.15 / 276.15 K) and the curve at that T gives P_sat(273.15) ~= 6.87 kPa vs the floor Pf = 6.3 kPa -- a small offset (~0.6 kPa) where the saturation curve starts above the floor. The clamps absorb this discrepancy in practice.

Gas-only substances: Helium has A = B = 0 which short-circuits both FreezingTemperature and MaxLiquidTemperature to TemperatureKelvin.Zero. MatterState(Helium) = Gas. Helium has no solid or liquid region on the (T, P) diagram; it is gas everywhere the simulation can express.

GasType enum (every state Stationeers tracks)

For reference, the full set of Chemistry.GasType values that participate in phase logic, as enumerated by the switches in Mole / MoleHelper:

Undefined,
Oxygen, Nitrogen, CarbonDioxide, Methane, Pollutant, Water, PollutedWater, NitrousOxide,
LiquidNitrogen, LiquidOxygen, LiquidMethane, Steam, LiquidCarbonDioxide, LiquidPollutant, LiquidNitrousOxide,
Hydrogen, LiquidHydrogen,
Hydrazine, LiquidHydrazine,
LiquidAlcohol,
Helium,
LiquidSodiumChloride,
Silanol, LiquidSilanol,
HydrochloricAcid, LiquidHydrochloricAcid,
Ozone, LiquidOzone

Volatiles (the pre-2026 name for methane) no longer appears as a separate GasType value; the rename to Methane is reflected throughout. There is no separate Steam constant table; Steam re-uses Water's A, B and critical temperature (line 424178 routes Steam to Chemistry.CRITICAL_TEMPERATURE_WATER_K).

Verification history

• 2026-05-14: page created from a fresh read of .work/decomp/0.2.6228.27061/Assembly-CSharp.decompiled.cs. All coefficients, switches, and reference pressures captured verbatim. Computed freeze and max-liquid temperatures via T = (P / A)^(1 / B) in PowerShell.
• 2026-05-15: added "Phase model" section documenting AtmosphereHelper.MatterState (no Solid value; freezing produces a PureIce Thing), the Chemistry.MatterState(GasType) classifier (Water and PollutedWater are Liquid; Steam is Gas), the pressure-independent Mole.WillFreeze() rule, the atmospheric freezing trigger in GlobalGasMix.StateChangeMoleQuantity, and the clamp semantics of EvaporationTemperatureClamped / EvaporationPressureClamped. Establishes the four phase-region boundaries on a (T, P) diagram: solid-liquid at vertical T = Tf, liquid-gas along P = A * T^B, critical wall at vertical T = Tmax_liq, and the small offset where Water's hardcoded Tf = 273.15 K puts the curve start ~0.6 kPa above the floor.

Open questions

• Whether the qwoa4qjloh Desmos calculator titled "Phase state diagram" implements this P = A * T^B form for all post-March-2026 gases. WebFetch cannot read the rendered curves, and the project's single Playwright instance was held by another session at the time of this writeup; visual confirmation pending.
• Whether the in-game Stationpedia phase-diagram pages use exactly this formula or a piecewise variant. The hardcoded water/polluted-water triple-point temperatures suggest at least one piecewise step exists at the curve-vs-floor boundary; the exact in-game render path was not traced.