diff --git a/Source/Engines/ModuleEnginesRF.cs b/Source/Engines/ModuleEnginesRF.cs
index 3fb435d7..dec462bb 100644
--- a/Source/Engines/ModuleEnginesRF.cs
+++ b/Source/Engines/ModuleEnginesRF.cs
@@ -54,7 +54,7 @@ public class ModuleEnginesRF : ModuleEnginesSolver
 
         protected Propellant curveProp;
 
-        [KSPField(guiName = "#RF_EngineRF_IgnitedFor", guiUnits = "s", guiFormat = "F3", groupName = groupName)] // Ignited for 
+        [KSPField(guiName = "#RF_EngineRF_IgnitedFor", guiUnits = "s", guiFormat = "F3", groupName = groupName)] // Ignited for
         public float curveTime = 0f;
         #endregion
 
@@ -496,9 +496,9 @@ private void SetFields()
                 tags += pressureFed ? ", " : string.Empty;
                 tags += $"<color=yellow>{Localizer.GetStringByTag("#RF_EngineRF_Ullage")}</color>"; // Ullage
             }
-            sISP = $"{atmosphereCurve.Evaluate(1):N0} (ASL) - {atmosphereCurve.Evaluate(0):N0} (Vac)"; // 
+            sISP = $"{atmosphereCurve.Evaluate(1):N0} (ASL) - {atmosphereCurve.Evaluate(0):N0} (Vac)"; //
             GetThrustData(out double thrustVac, out double thrustASL);
-            sThrust = $"{Utilities.FormatThrust(thrustASL)} (ASL) - {Utilities.FormatThrust(thrustVac)} (Vac)"; // 
+            sThrust = $"{Utilities.FormatThrust(thrustASL)} (ASL) - {Utilities.FormatThrust(thrustVac)} (Vac)"; //
             if (ignitions > 0)
                 sIgnitions = $"{ignitions:N0}";
             else if (ignitions == -1)
@@ -685,9 +685,8 @@ public override void UpdateSolver(EngineThermodynamics ambientTherm, double alti
                 {
                     if (EngineIgnited && ignited && throttledUp && rfSolver.GetRunning())
                     {
-                        double state = ullageSet.GetUllageStability();
-                        double testValue = Math.Pow(state, RFSettings.Instance.stabilityPower);
-                        if (staticRandom.NextDouble() > testValue)
+                        double ullageProbability = ullageSet.GetUllageProbability();
+                        if (staticRandom.NextDouble() > ullageProbability)
                         {
                             ScreenMessages.PostScreenMessage(ullageFail);
                             FlightLogger.fetch.LogEvent($"[{FormatTime(vessel.missionTime)}] {ullageFail.message}");
@@ -762,10 +761,10 @@ public void SetScale(double newScale)
         #region Info
         protected string ThrottleString()
         {
-            if (throttleLocked) { return ", throttle locked"; } // 
-            if (MinThrottle == 1f) { return ", unthrottleable"; } // 
+            if (throttleLocked) { return ", throttle locked"; } //
+            if (MinThrottle == 1f) { return ", unthrottleable"; } //
             if (MinThrottle < 0f || MinThrottle > 1f) { return string.Empty; }
-            return $", {MinThrottle:P0} min throttle"; // 
+            return $", {MinThrottle:P0} min throttle"; //
         }
 
         protected void GetThrustData(out double thrustVac, out double thrustASL)
@@ -850,8 +849,8 @@ protected string GetThrustInfo()
                     output += $"{MinThrottle:P0} {Localizer.GetStringByTag("#RF_EngineRF_MinThrottle")}\n"; // min throttle
                     if (thrustASL != thrustVac)
                     {
-                        output += $"<b>{Localizer.GetStringByTag("#RF_EngineRF_MAXThrustInVac")}: </b>{Utilities.FormatThrust(thrustVac)} (TWR {thrustVac / weight:0.0##})\n"; //Max. Thrust (Vac) 
-                        output += $"<b>{Localizer.GetStringByTag("#RF_EngineRF_MAXThrustInASL")}: </b>{Utilities.FormatThrust(thrustASL)} (TWR {thrustASL / weight:0.0##})\n"; //Max. Thrust (ASL) 
+                        output += $"<b>{Localizer.GetStringByTag("#RF_EngineRF_MAXThrustInVac")}: </b>{Utilities.FormatThrust(thrustVac)} (TWR {thrustVac / weight:0.0##})\n"; //Max. Thrust (Vac)
+                        output += $"<b>{Localizer.GetStringByTag("#RF_EngineRF_MAXThrustInASL")}: </b>{Utilities.FormatThrust(thrustASL)} (TWR {thrustASL / weight:0.0##})\n"; //Max. Thrust (ASL)
                         output += $"<b>{Localizer.GetStringByTag("#RF_EngineRF_MINThrustInVac")}: </b>{Utilities.FormatThrust(thrustVac * MinThrottle)} (TWR {thrustVac * MinThrottle / weight:0.0##})\n"; // Min. Thrust (Vac)
                         output += $"<b>{Localizer.GetStringByTag("#RF_EngineRF_MINThrustInASL")}: </b>{Utilities.FormatThrust(thrustASL * MinThrottle)} (TWR {thrustASL * MinThrottle / weight:0.0##})\n"; // Min. Thrust (ASL)
                     }
@@ -887,7 +886,7 @@ public string GetUllageIgnition()
             return output;
         }
 
-        
+
         public override string GetInfo()
         {
             string output = $"{GetThrustInfo()}" +
diff --git a/Source/Ullage/UllageSet.cs b/Source/Ullage/UllageSet.cs
index b07af9d6..aa490064 100644
--- a/Source/Ullage/UllageSet.cs
+++ b/Source/Ullage/UllageSet.cs
@@ -119,7 +119,7 @@ public void Update(Vector3 acc, Vector3 angVel, double timeDelta, double venting
                 angularVelocity = engine.transform.InverseTransformDirection(engine.part.rb.angularVelocity);
             else
                 angularVelocity = engine.transform.InverseTransformDirection(angVel);
-            
+
             fuelRatio = 1d;
             if(HighLogic.LoadedSceneIsFlight && engine.EngineIgnited)
             {
@@ -139,6 +139,7 @@ public void Update(Vector3 acc, Vector3 angVel, double timeDelta, double venting
         public void SetUllageStability(double newStability) => ullageSim.SetPropellantStability(newStability);
         public string GetUllageState(out Color col) => ullageSim.GetPropellantStatus(out col);
         public double GetUllageStability() => ullageSim.GetPropellantStability();
+        public double GetUllageProbability() => ullageSim.GetPropellantProbability();
         public bool PressureOK() => !engine.pressureFed || tanksHighlyPressurized;
         public bool EditorPressurized()
         {
diff --git a/Source/Ullage/UllageSimulator.cs b/Source/Ullage/UllageSimulator.cs
index ce1ee860..86a6d270 100644
--- a/Source/Ullage/UllageSimulator.cs
+++ b/Source/Ullage/UllageSimulator.cs
@@ -105,7 +105,7 @@ public void Update(Vector3d localAcceleration, Vector3d rotation, double deltaTi
 
             //if (ventingAcc != 0.0f) Debug.Log("BoilOffAcc: " + ventingAcc.ToString("F8"));
             //else Debug.Log("BoilOffAcc: No boiloff.");
-            
+
             Vector3d localAccelerationAmount = localAcceleration * deltaTime;
             Vector3d rotationAmount = rotation * deltaTime;
 
@@ -179,8 +179,6 @@ public void Update(Vector3d localAcceleration, Vector3d rotation, double deltaTi
             //Debug.Log("Ullage: pHorizontal: " + pHorizontal.ToString("F3"));
 
             propellantStability = Math.Max(0.0d, 1.0d - (pVertical * pHorizontal * (0.75d + Math.Sqrt(bLevel))));
-            if (propellantStability >= veryStable)
-                propellantStability = 1d;
 
 //#if DEBUG
 //            if (propellantStability < 0.5d)
@@ -204,9 +202,15 @@ private void SetStateString()
                 propellantStatus = Localizer.GetStringByTag("#RF_UllageState_Unstable"); // "Unstable"
             else
                 propellantStatus = Localizer.GetStringByTag("#RF_UllageState_VeryUnstable"); // "Very Unstable"
-            propellantStatus += $" ({propellantStability:P2})";
+            propellantStatus += $" ({GetPropellantProbability():P2})";
         }
         public double GetPropellantStability() => propellantStability;
+        public double GetPropellantProbability()
+        {
+            // round up veryStable (>= 0.996) to 100% stable
+            double stability = propellantStability >= veryStable ? 1.0d : propellantStability;
+            return Math.Pow(stability, RFSettings.Instance.stabilityPower);
+        }
         public void SetPropellantStability(double newStab) => propellantStability = newStab;
         public string GetPropellantStatus(out Color col)
         {