diff --git a/AdventOfCode.lpi b/AdventOfCode.lpi
index dbeeb5b..8cebdb5 100644
--- a/AdventOfCode.lpi
+++ b/AdventOfCode.lpi
@@ -77,6 +77,10 @@
         <Filename Value="solvers\UPipeMaze.pas"/>
         <IsPartOfProject Value="True"/>
       </Unit>
+      <Unit>
+        <Filename Value="solvers\UCosmicExpansion.pas"/>
+        <IsPartOfProject Value="True"/>
+      </Unit>
     </Units>
   </ProjectOptions>
   <CompilerOptions>
diff --git a/AdventOfCode.lpr b/AdventOfCode.lpr
index e80b665..9bda50e 100644
--- a/AdventOfCode.lpr
+++ b/AdventOfCode.lpr
@@ -26,7 +26,7 @@ uses
   Classes, SysUtils, CustApp,
   USolver,
   UTrebuchet, UCubeConundrum, UGearRatios, UScratchcards, UGiveSeedFertilizer, UWaitForIt, UCamelCards,
-  UHauntedWasteland, UNumberTheory, UMirageMaintenance, UPipeMaze;
+  UHauntedWasteland, UNumberTheory, UMirageMaintenance, UPipeMaze, UCosmicExpansion;
 
 type
 
@@ -61,6 +61,7 @@ begin
   engine.RunAndFree(THauntedWasteland.Create);
   engine.RunAndFree(TMirageMaintenance.Create);
   engine.RunAndFree(TPipeMaze.Create);
+  engine.RunAndFree(TCosmicExpansion.Create);
   engine.Free;
 end;
 
diff --git a/solvers/UCosmicExpansion.pas b/solvers/UCosmicExpansion.pas
new file mode 100644
index 0000000..6f9ba96
--- /dev/null
+++ b/solvers/UCosmicExpansion.pas
@@ -0,0 +1,127 @@
+{
+  Solutions to the Advent Of Code.
+  Copyright (C) 2023  Stefan Müller
+
+  This program is free software: you can redistribute it and/or modify it under
+  the terms of the GNU General Public License as published by the Free Software
+  Foundation, either version 3 of the License, or (at your option) any later
+  version.
+
+  This program is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+  FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License along with
+  this program.  If not, see <http://www.gnu.org/licenses/>.
+}
+
+unit UCosmicExpansion;
+
+{$mode ObjFPC}{$H+}
+
+interface
+
+uses
+  Classes, SysUtils, Generics.Collections, Math, USolver;
+
+const
+  CGalaxyChar = '#';
+  CEmptySpaceFactor = 2;
+  CNonEmptySpaceFactor = 1;
+
+type
+
+  { TCosmicExpansion }
+
+  TCosmicExpansion = class(TSolver)
+  private
+    FColumnExpansion, FRowExpansion: specialize TList<Integer>;
+    FGalaxies: specialize TList<TPoint>;
+    procedure InitColumnExpansion(const ASize: Integer);
+  public
+    constructor Create;
+    destructor Destroy; override;
+    procedure ProcessDataLine(const ALine: string); override;
+    procedure Finish; override;
+    function GetDataFileName: string; override;
+    function GetPuzzleName: string; override;
+  end;
+
+implementation
+
+{ TCosmicExpansion }
+
+procedure TCosmicExpansion.InitColumnExpansion(const ASize: Integer);
+var
+  i: Integer;
+begin
+  if FColumnExpansion.Count = 0 then
+  begin
+    FColumnExpansion.Capacity := ASize;
+    for i := 1 to ASize do
+      FColumnExpansion.Add(CEmptySpaceFactor);
+  end;
+end;
+
+constructor TCosmicExpansion.Create;
+begin
+  FColumnExpansion := specialize TList<Integer>.Create;
+  FRowExpansion := specialize TList<Integer>.Create;
+  FGalaxies := specialize TList<TPoint>.Create;
+end;
+
+destructor TCosmicExpansion.Destroy;
+begin
+  FColumnExpansion.Free;
+  FRowExpansion.Free;
+  FGalaxies.Free;
+  inherited Destroy;
+end;
+
+procedure TCosmicExpansion.ProcessDataLine(const ALine: string);
+var
+  empty: Boolean;
+  i : Integer;
+begin
+  InitColumnExpansion(Length(ALine));
+
+  empty := True;
+  for i := 1 to Length(ALine) do
+    if ALine[i] = CGalaxyChar then
+    begin
+      FGalaxies.Add(Point(i, FRowExpansion.Count));
+      empty := False;
+      FColumnExpansion[i - 1] := CNonEmptySpaceFactor;
+    end;
+
+  if empty then
+    FRowExpansion.Add(CEmptySpaceFactor)
+  else
+    FRowExpansion.Add(CNonEmptySpaceFactor);
+end;
+
+procedure TCosmicExpansion.Finish;
+var
+  i, j, k: Integer;
+begin
+  for i := 0 to FGalaxies.Count - 1 do
+    for j := i + 1 to FGalaxies.Count - 1 do begin
+      for k := Min(FGalaxies[i].X, FGalaxies[j].X) to Max(FGalaxies[i].X, FGalaxies[j].X) - 1 do
+        Inc(FPart1, FColumnExpansion[k]);
+      for k := Min(FGalaxies[i].Y, FGalaxies[j].Y) + 1 to Max(FGalaxies[i].Y, FGalaxies[j].Y) do
+        Inc(FPart1, FRowExpansion[k]);
+    end;
+end;
+
+function TCosmicExpansion.GetDataFileName: string;
+begin
+  Result := 'cosmic_expansion.txt';
+end;
+
+function TCosmicExpansion.GetPuzzleName: string;
+begin
+   Result := 'Day 11: Cosmic Expansion';
+end;
+
+end.
+
diff --git a/tests/AdventOfCodeFPCUnit.lpi b/tests/AdventOfCodeFPCUnit.lpi
index 46f8cdf..3875c21 100644
--- a/tests/AdventOfCodeFPCUnit.lpi
+++ b/tests/AdventOfCodeFPCUnit.lpi
@@ -84,6 +84,10 @@
         <Filename Value="UPipeMazeTestCases.pas"/>
         <IsPartOfProject Value="True"/>
       </Unit>
+      <Unit>
+        <Filename Value="UCosmicExpansionTestCases.pas"/>
+        <IsPartOfProject Value="True"/>
+      </Unit>
     </Units>
   </ProjectOptions>
   <CompilerOptions>
diff --git a/tests/AdventOfCodeFPCUnit.lpr b/tests/AdventOfCodeFPCUnit.lpr
index 2697a07..3a607b4 100644
--- a/tests/AdventOfCodeFPCUnit.lpr
+++ b/tests/AdventOfCodeFPCUnit.lpr
@@ -5,7 +5,7 @@ program AdventOfCodeFPCUnit;
 uses
   Interfaces, Forms, GuiTestRunner, USolver, UBaseTestCases, UTrebuchetTestCases, UCubeConundrumTestCases,
   UGearRatiosTestCases, UScratchcardsTestCases, UGiveSeedFertilizerTestCases, UWaitForItTestCases, UCamelCardsTestCases,
-  UHauntedWastelandTestCases, UMirageMaintenanceTestCases, UPipeMazeTestCases;
+  UHauntedWastelandTestCases, UMirageMaintenanceTestCases, UPipeMazeTestCases, UCosmicExpansionTestCases;
 
 {$R *.res}
 
diff --git a/tests/UCosmicExpansionTestCases.pas b/tests/UCosmicExpansionTestCases.pas
new file mode 100644
index 0000000..4093e91
--- /dev/null
+++ b/tests/UCosmicExpansionTestCases.pas
@@ -0,0 +1,78 @@
+{
+  Solutions to the Advent Of Code.
+  Copyright (C) 2023  Stefan Müller
+
+  This program is free software: you can redistribute it and/or modify it under
+  the terms of the GNU General Public License as published by the Free Software
+  Foundation, either version 3 of the License, or (at your option) any later
+  version.
+
+  This program is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+  FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License along with
+  this program.  If not, see <http://www.gnu.org/licenses/>.
+}
+
+unit UCosmicExpansionTestCases;
+
+{$mode ObjFPC}{$H+}
+
+interface
+
+uses
+  Classes, SysUtils, fpcunit, testregistry, USolver, UBaseTestCases, UCosmicExpansion;
+
+type
+
+  { TCosmicExpansionFullDataTestCase }
+
+  TCosmicExpansionFullDataTestCase = class(TEngineBaseTest)
+  protected
+    function CreateSolver: ISolver; override;
+  published
+    procedure TestPart1;
+  end;
+
+  { TCosmicExpansionExampleTestCase }
+
+  TCosmicExpansionExampleTestCase = class(TExampleEngineBaseTest)
+  protected
+    function CreateSolver: ISolver; override;
+  published
+    procedure TestPart1;
+  end;
+
+implementation
+
+{ TCosmicExpansionFullDataTestCase }
+
+function TCosmicExpansionFullDataTestCase.CreateSolver: ISolver;
+begin
+  Result := TCosmicExpansion.Create;
+end;
+
+procedure TCosmicExpansionFullDataTestCase.TestPart1;
+begin
+  AssertEquals(9686930, FSolver.GetResultPart1);
+end;
+
+{ TCosmicExpansionExampleTestCase }
+
+function TCosmicExpansionExampleTestCase.CreateSolver: ISolver;
+begin
+  Result := TCosmicExpansion.Create;
+end;
+
+procedure TCosmicExpansionExampleTestCase.TestPart1;
+begin
+  AssertEquals(374, FSolver.GetResultPart1);
+end;
+
+initialization
+
+  RegisterTest(TCosmicExpansionFullDataTestCase);
+  RegisterTest(TCosmicExpansionExampleTestCase);
+end.
+