diff --git a/ClosedXML/Excel/CalcEngine/XLCalcEngine.cs b/ClosedXML/Excel/CalcEngine/XLCalcEngine.cs
index e7457e2..6686621 100644
--- a/ClosedXML/Excel/CalcEngine/XLCalcEngine.cs
+++ b/ClosedXML/Excel/CalcEngine/XLCalcEngine.cs
@@ -27,14 +27,36 @@
         {
             if (identifier.Contains("!") && _wb != null)
             {
-                var wsName = identifier.Substring(0, identifier.IndexOf("!"));
-                return new CellRangeReference(_wb.Worksheet(wsName).Range(identifier.Substring(identifier.IndexOf("!") + 1)), this);
+                var referencedSheetNames = identifier.Split(':')
+                    .Select(part =>
+                    {
+                        if (part.Contains("!"))
+                            return part.Substring(0, part.IndexOf('!')).ToLower();
+                        else
+                            return null;
+                    })
+                    .Where(sheet => sheet != null)
+                    .Distinct();
+
+                if (!referencedSheetNames.Any())
+                    return new CellRangeReference(_ws.Range(identifier), this);
+                else if (referencedSheetNames.Count() > 1)
+                    throw new ArgumentOutOfRangeException(referencedSheetNames.Last(), "Cross worksheet references may references no more than 1 other worksheet");
+                else
+                {
+                    IXLWorksheet worksheet;
+                    if (!_wb.TryGetWorksheet(referencedSheetNames.Single(), out worksheet))
+                        throw new ArgumentOutOfRangeException(referencedSheetNames.Single(), "The required worksheet cannot be found");
+
+                    identifier = identifier.ToLower().Replace(string.Format("{0}!", worksheet.Name.ToLower()), "");
+
+                    return new CellRangeReference(worksheet.Range(identifier), this);
+                }
             }
-
-            if (_ws != null)
+            else if (_ws != null)
                 return new CellRangeReference(_ws.Range(identifier), this);
-
-            return identifier;
+            else
+                return identifier;
         }
     }
 
diff --git a/ClosedXML/Excel/XLWorkbook.cs b/ClosedXML/Excel/XLWorkbook.cs
index a33adcc..645d536 100644
--- a/ClosedXML/Excel/XLWorkbook.cs
+++ b/ClosedXML/Excel/XLWorkbook.cs
@@ -396,7 +396,7 @@
 
         public Boolean TryGetWorksheet(String name, out IXLWorksheet worksheet)
         {
-            if (Worksheets.Any(w => w.Name.ToLower().Equals(name.ToLower())))
+            if (Worksheets.Any(w => string.Equals(w.Name, XLWorksheets.TrimSheetName(name), StringComparison.OrdinalIgnoreCase)))
             {
                 worksheet = Worksheet(name);
                 return true;
diff --git a/ClosedXML/Excel/XLWorksheets.cs b/ClosedXML/Excel/XLWorksheets.cs
index ee17781..6207f57 100644
--- a/ClosedXML/Excel/XLWorksheets.cs
+++ b/ClosedXML/Excel/XLWorksheets.cs
@@ -56,17 +56,24 @@
             return false;
         }
 
-        public IXLWorksheet Worksheet(String sheetName)
+        internal static string TrimSheetName(string sheetName)
         {
-            XLWorksheet w;
             if (sheetName.StartsWith("'") && sheetName.EndsWith("'") && sheetName.Length > 2)
                 sheetName = sheetName.Substring(1, sheetName.Length - 2);
 
+            return sheetName;
+        }
+
+        public IXLWorksheet Worksheet(String sheetName)
+        {
+            sheetName = TrimSheetName(sheetName);
+
+            XLWorksheet w;
+
             if (_worksheets.TryGetValue(sheetName, out w))
                 return w;
 
-            var wss = _worksheets.Where(ws => ws.Key.ToLower().Equals(sheetName.ToLower()));
-
+            var wss = _worksheets.Where(ws => string.Equals(ws.Key, sheetName, StringComparison.OrdinalIgnoreCase));
             if (wss.Any())
                 return wss.First().Value;
 
diff --git a/ClosedXML_Tests/Excel/Misc/FormulaTests.cs b/ClosedXML_Tests/Excel/Misc/FormulaTests.cs
index a1e1a66..9cfaf7e 100644
--- a/ClosedXML_Tests/Excel/Misc/FormulaTests.cs
+++ b/ClosedXML_Tests/Excel/Misc/FormulaTests.cs
@@ -1,6 +1,7 @@
 using ClosedXML.Excel;
 using NUnit.Framework;
 using System;
+using System.Linq;
 
 namespace ClosedXML_Tests.Excel
 {
@@ -63,6 +64,47 @@
         }
 
         [Test]
+        public void FormulaWithReferenceIncludingSheetName()
+        {
+            using (var wb = new XLWorkbook())
+            {
+                object value;
+                var ws = wb.AddWorksheet("Sheet1");
+                ws.Cell("A1").InsertData(Enumerable.Range(1, 50));
+                ws.Cell("B1").FormulaA1 = "=SUM(A1:A50)";
+                value = ws.Cell("B1").Value;
+                Assert.AreEqual(1275, value);
+
+                ws = wb.AddWorksheet("Sheet2");
+
+                ws.Cell("A1").FormulaA1 = "=SUM(Sheet1!A1:Sheet1!A50)";
+                value = ws.Cell("A1").Value;
+                Assert.AreEqual(1275, value);
+
+                ws.Cell("B1").FormulaA1 = "=SUM(Sheet1!A1:A50)";
+                value = ws.Cell("B1").Value;
+                Assert.AreEqual(1275, value);
+            }
+        }
+
+        [Test]
+        public void InvalidReferences()
+        {
+            using (var wb = new XLWorkbook())
+            {
+                var ws = wb.AddWorksheet("Sheet1");
+                ws.Cell("A1").InsertData(Enumerable.Range(1, 50));
+                ws = wb.AddWorksheet("Sheet2");
+
+                ws.Cell("A1").FormulaA1 = "=SUM(Sheet1!A1:Sheet2!A50)";
+                Assert.That(() => ws.Cell("A1").Value, Throws.InstanceOf<ArgumentOutOfRangeException>());
+
+                ws.Cell("B1").FormulaA1 = "=SUM(Sheet1!A1:UnknownSheet!A50)";
+                Assert.That(() => ws.Cell("B1").Value, Throws.InstanceOf<ArgumentOutOfRangeException>());
+            }
+        }
+
+        [Test]
         public void DateAgainstStringComparison()
         {
             using (var wb = new XLWorkbook())