diff --git a/components/fpspreadsheet/fpsopendocument.pas b/components/fpspreadsheet/fpsopendocument.pas
index 4dc69b4f2..244f1c05d 100755
--- a/components/fpspreadsheet/fpsopendocument.pas
+++ b/components/fpspreadsheet/fpsopendocument.pas
@@ -30,7 +30,7 @@ uses
   Classes, SysUtils,
   fpszipper, {NOTE: fpszipper is the latest zipper.pp Change to standard zipper when FPC 2.4 is released. Changed by JLJR}
   fpspreadsheet,
-  xmlread, DOM;
+  xmlread, DOM, AVL_Tree;
   
 type
 
@@ -404,6 +404,8 @@ var
   CurCell: PCell;
   CurRow: array of PCell;
   LastColNum: Cardinal;
+  ACell: PCell;
+  AVLNode: TAVLTreeNode;
 begin
   LastColNum := CurSheet.GetLastColNumber;
 
@@ -413,41 +415,30 @@ begin
   '      <table:table-column table:style-name="co1" table:number-columns-repeated="' +
   IntToStr(LastColNum + 1) + '" table:default-cell-style-name="Default"/>' + LineEnding;
 
+  ACell := GetMem(SizeOf(TCell));
+
   // The cells need to be written in order, row by row, cell by cell
   for j := 0 to CurSheet.GetLastRowNumber do
   begin
     FContent := FContent +
     '      <table:table-row table:style-name="ro1">' + LineEnding;
 
-    // First make an array with the cells of this row in their respective order
-    // nil pointers indicate empty cells, so it's necessary to initialize the array
-    SetLength(CurRow, LastColNum + 1);
-    for k := 0 to LastColNum do CurRow[k] := nil;
-
-    // Now fill the array with the cells in their proper place
-    for k := 0 to CurSheet.FCells.Count - 1 do
-    begin
-      CurCell := CurSheet.FCells.Items[k];
-      if CurCell^.Row = j then CurRow[CurCell^.Col] := CurCell;
-    end;
-
-    // And now write all cells from this row
+    // Write cells from this row.
     for k := 0 to LastColNum do
     begin
-      CurCell := CurRow[k];
-
-      if CurCell = nil then
-        FContent := FContent + '<table:table-cell/>' + LineEnding
-      else WriteCellCallback(CurCell, nil);
+      ACell^.Row := j;
+      ACell^.Col := k;
+      AVLNode := CurSheet.Cells.Find(ACell);
+      if Assigned(AVLNode) then
+        WriteCellCallback(PCell(AVLNode.Data), nil)
+      else
+        FContent := FContent + '<table:table-cell/>' + LineEnding;
     end;
 
     FContent := FContent +
     '      </table:table-row>' + LineEnding;
   end;
 
-  // Clean up
-  SetLength(CurRow, 0);
-
   // Footer
   FContent := FContent +
   '    </table:table>' + LineEnding;
diff --git a/components/fpspreadsheet/fpspreadsheet.pas b/components/fpspreadsheet/fpspreadsheet.pas
index 83278799c..abd0cbb61 100755
--- a/components/fpspreadsheet/fpspreadsheet.pas
+++ b/components/fpspreadsheet/fpspreadsheet.pas
@@ -14,7 +14,7 @@ unit fpspreadsheet;
 interface
 
 uses
-  Classes, SysUtils;
+  Classes, SysUtils, AVL_Tree;
 
 type
   TsSpreadsheetFormat = (sfExcel2, sfExcel3, sfExcel4, sfExcel5, sfExcel8,
@@ -98,9 +98,9 @@ type
 
   TsWorksheet = class
   private
+    FCells: TAvlTree;
     procedure RemoveCallback(data, arg: pointer);
   public
-    FCells: TFPList;
     Name: string;
     { Base methods }
     constructor Create;
@@ -109,7 +109,6 @@ type
     function  FindCell(ARow, ACol: Cardinal): PCell;
     function  GetCell(ARow, ACol: Cardinal): PCell;
     function  GetCellCount: Cardinal;
-    function  GetCellByIndex(AIndex: Cardinal): PCell;
     function  GetLastColNumber: Cardinal;
     function  GetLastRowNumber: Cardinal;
     function  ReadAsUTF8Text(ARow, ACol: Cardinal): ansistring;
@@ -118,6 +117,7 @@ type
     procedure WriteNumber(ARow, ACol: Cardinal; ANumber: double);
     procedure WriteFormula(ARow, ACol: Cardinal; AFormula: TsFormula);
     procedure WriteRPNFormula(ARow, ACol: Cardinal; AFormula: TsRPNFormula);
+    property  Cells: TAVLTree read FCells;
   end;
 
   { TsWorkbook }
@@ -178,7 +178,7 @@ type
     function  ExpandFormula(AFormula: TsFormula): TsExpandedFormula;
     { General writing methods }
     procedure WriteCellCallback(data, arg: pointer);
-    procedure WriteCellsToStream(AStream: TStream; ACells: TFPList);
+    procedure WriteCellsToStream(AStream: TStream; ACells: TAVLTree);
     procedure WriteToFile(AFileName: string; AData: TsWorkbook); virtual;
     procedure WriteToStream(AStream: TStream; AData: TsWorkbook); virtual;
     { Record writing methods }
@@ -206,6 +206,9 @@ procedure RegisterSpreadFormat(
 
 implementation
 
+uses
+  Math;
+
 var
   { Translatable strings }
   lpUnsupportedReadFormat, lpUnsupportedWriteFormat: string;
@@ -241,6 +244,13 @@ begin
   FreeMem(data);
 end;
 
+function CompareCells(Item1, Item2: Pointer): Integer;
+begin
+  result := PCell(Item1).Row - PCell(Item2).Row;
+  if Result = 0 then
+    Result := PCell(Item1).Col - PCell(Item2).Col;
+end;
+
 {@@
   Constructor.
 }
@@ -248,7 +258,7 @@ constructor TsWorksheet.Create;
 begin
   inherited Create;
 
-  FCells := TFPList.Create;
+  FCells := TAVLTree.Create(@CompareCells);
 end;
 
 {@@
@@ -277,24 +287,16 @@ end;
 }
 function TsWorksheet.FindCell(ARow, ACol: Cardinal): PCell;
 var
-  i: Integer;
-  ACell: PCell;
+  LCell: TCell;
+  AVLNode: TAVLTreeNode;
 begin
-  i := 0;
   Result := nil;
-  
-  while (i < FCells.Count) do
-  begin
-    ACell := PCell(FCells.Items[i]);
-    
-    if (ACell^.Row = ARow) and (ACell^.Col = ACol) then
-    begin
-      Result := ACell;
-      Exit;
-    end;
-    
-    Inc(i);
-  end;
+
+  LCell.Row := ARow;
+  LCell.Col := ACol;
+  AVLNode := Cells.Find(@LCell);
+  if Assigned(AVLNode) then
+    result := PCell(AVLNode.Data);
 end;
 
 {@@
@@ -326,7 +328,7 @@ begin
     Result^.Row := ARow;
     Result^.Col := ACol;
 
-    FCells.Add(Result);
+    Cells.Add(Result);
   end;
 end;
 
@@ -343,28 +345,7 @@ end;
 }
 function TsWorksheet.GetCellCount: Cardinal;
 begin
-  Result := FCells.Count;
-end;
-
-{@@
-  Obtains the cell with a specific index in the internal list of cells.
-
-  The index goes from 0 to GetCellCount - 1.
-
-  This routine is used together with GetCellCount to
-  iterate througth all cells in a worksheet efficiently.
-
-  @param  AIndex    The index of the cell to be obtained
-
-  @return A pointer to the cell, or nil if it doesn't exist
-
-  @see    TCell
-  @see    GetCellCount
-}
-function TsWorksheet.GetCellByIndex(AIndex: Cardinal): PCell;
-begin
-  if FCells.Count > AIndex then Result := PCell(FCells.Items[AIndex])
-  else Result := nil;
+  Result := Cells.Count;
 end;
 
 {@@
@@ -379,19 +360,18 @@ end;
 }
 function TsWorksheet.GetLastColNumber: Cardinal;
 var
-  i: Integer;
-  ACell: PCell;
+  AVLNode: TAVLTreeNode;
 begin
-  i := 0;
   Result := 0;
 
-  while (i < FCells.Count) do
+  // Traverse the tree from lowest to highest.
+  // Since tree primary sort order is on Row
+  // highest Col could exist anywhere.
+  AVLNode := Cells.FindLowest;
+  While Assigned(AVLNode) do
   begin
-    ACell := PCell(FCells.Items[i]);
-
-    if ACell^.Col > Result then Result := ACell^.Col;
-
-    Inc(i);
+    Result := Math.Max(Result, PCell(AVLNode.Data)^.Col);
+    AVLNode := Cells.FindSuccessor(AVLNode);
   end;
 end;
 
@@ -407,20 +387,13 @@ end;
 }
 function TsWorksheet.GetLastRowNumber: Cardinal;
 var
-  i: Integer;
-  ACell: PCell;
+  AVLNode: TAVLTreeNode;
 begin
-  i := 0;
   Result := 0;
 
-  while (i < FCells.Count) do
-  begin
-    ACell := PCell(FCells.Items[i]);
-
-    if ACell^.Row > Result then Result := ACell^.Row;
-
-    Inc(i);
-  end;
+  AVLNode := FCells.FindHighest;
+  if Assigned(AVLNode) then
+    Result := PCell(AVLNode.Data).Row;
 end;
 
 {@@
@@ -460,8 +433,16 @@ end;
   Clears the list of Cells and releases their memory.
 }
 procedure TsWorksheet.RemoveAllCells;
+var
+  Node: TAVLTreeNode;
 begin
-  FCells.ForEachCall(RemoveCallback, nil);
+  Node:=FCells.FindLowest;
+  while Assigned(Node) do begin
+    RemoveCallback(Node.Data,nil);
+    Node.Data:=nil;
+    Node:=FCells.FindSuccessor(Node);
+  end;
+  FCells.Clear;
 end;
 
 {@@
@@ -725,7 +706,7 @@ end;
 }
 function TsWorkbook.GetWorksheetByIndex(AIndex: Cardinal): TsWorksheet;
 begin
-  if AIndex < FWorksheets.Count then Result := TsWorksheet(FWorksheets.Items[AIndex])
+  if (integer(AIndex) < FWorksheets.Count) and (integer(AIndex)>=0) then Result := TsWorksheet(FWorksheets.Items[AIndex])
   else Result := nil;
 end;
 
@@ -854,9 +835,16 @@ end;
   @param  AStream The output stream.
   @param  ACells  List of cells to be writeen
 }
-procedure TsCustomSpreadWriter.WriteCellsToStream(AStream: TStream; ACells: TFPList);
+procedure TsCustomSpreadWriter.WriteCellsToStream(AStream: TStream; ACells: TAVLTree);
+var
+  AVLNode: TAVLTreeNode;
 begin
-  ACells.ForEachCall(WriteCellCallback, Pointer(AStream));
+  AVLNode := ACells.FindLowest;
+  While Assigned(AVLNode) do
+  begin
+    WriteCellCallback(AVLNode.Data, Pointer(AStream));
+    AVLNode := ACells.FindSuccessor(AVLNode);
+  end;
 end;
 
 {@@
diff --git a/components/fpspreadsheet/xlsbiff2.pas b/components/fpspreadsheet/xlsbiff2.pas
index 3347042a5..544d0e012 100755
--- a/components/fpspreadsheet/xlsbiff2.pas
+++ b/components/fpspreadsheet/xlsbiff2.pas
@@ -130,7 +130,7 @@ procedure TsSpreadBIFF2Writer.WriteToStream(AStream: TStream; AData: TsWorkbook)
 begin
   WriteBOF(AStream);
 
-  WriteCellsToStream(AStream, AData.GetFirstWorksheet.FCells);
+  WriteCellsToStream(AStream, AData.GetFirstWorksheet.Cells);
 
   WriteEOF(AStream);
 end;
diff --git a/components/fpspreadsheet/xlsbiff5.pas b/components/fpspreadsheet/xlsbiff5.pas
index 6f94c8a53..e8306a540 100755
--- a/components/fpspreadsheet/xlsbiff5.pas
+++ b/components/fpspreadsheet/xlsbiff5.pas
@@ -403,7 +403,7 @@ begin
 
     WriteWindow2(AStream, True);
 
-    WriteCellsToStream(AStream, AData.GetWorksheetByIndex(i).FCells);
+    WriteCellsToStream(AStream, AData.GetWorksheetByIndex(i).Cells);
 
     WriteEOF(AStream);
   end;
diff --git a/components/fpspreadsheet/xlsbiff8.pas b/components/fpspreadsheet/xlsbiff8.pas
index dfa35b323..2af8dd5af 100755
--- a/components/fpspreadsheet/xlsbiff8.pas
+++ b/components/fpspreadsheet/xlsbiff8.pas
@@ -370,7 +370,7 @@ begin
 
     WriteWindow2(AStream, True);
 
-    WriteCellsToStream(AStream, AData.GetWorksheetByIndex(i).FCells);
+    WriteCellsToStream(AStream, AData.GetWorksheetByIndex(i).Cells);
 
     WriteEOF(AStream);
   end;