diff --git a/lib/facter/esx_version.rb b/lib/facter/esx_version.rb
new file mode 100644
index 0000000..047fd65
--- /dev/null
+++ b/lib/facter/esx_version.rb
@@ -0,0 +1,42 @@
+require 'facter'
+
+# Author: Francois Deppierraz <francois.deppierraz@nimag.net>
+# Idea and address/version mapping comes from
+# http://virtwo.blogspot.ch/2010/10/which-esx-version-am-i-running-on.html
+
+Facter.add(:esx_version) do
+  confine :virtual => :vmware
+  setcode do
+    if File::executable?("/usr/sbin/dmidecode")
+      result = Facter::Util::Resolution.exec("/usr/sbin/dmidecode 2>&1")
+      if result
+        begin
+          bios_address = /^BIOS Information$.+?Address: (0x[0-9A-F]{5})$/m.match(result)[1]
+
+          case bios_address
+            when '0xE8480'
+              '2.5'
+            when '0xE7C70'
+              '3.0'
+            when '0xE7910'
+              '3.5'
+            when '0xEA6C0'
+              '4'
+            when '0xEA550'
+              '4 update 1'
+            when '0xEA2E0'
+              '4.1'
+            when '0xE72C0'
+              '5'
+            when '0xEA0C0'
+              '5.1'
+            else
+              "unknown, please report #{bios_address}"
+          end
+        rescue
+          'n/a'
+        end
+      end
+    end
+  end
+end