Index: src/NHibernate/Dialect/Oracle9Dialect.cs
===================================================================
--- src/NHibernate/Dialect/Oracle9Dialect.cs	(revision 3695)
+++ src/NHibernate/Dialect/Oracle9Dialect.cs	(working copy)
@@ -55,7 +55,7 @@
 			// having problems with both ODP and OracleClient from MS not being able
 			// to read values out of a field that is DOUBLE PRECISION
 			RegisterColumnType(DbType.Double, "DOUBLE PRECISION"); //"FLOAT(53)" );
-			//RegisterColumnType(DbType.Guid, "CHAR(38)");
+			RegisterColumnType(DbType.Guid, "RAW(16)");
 			RegisterColumnType(DbType.Int16, "NUMBER(5,0)");
 			RegisterColumnType(DbType.Int32, "NUMBER(10,0)");
 			RegisterColumnType(DbType.Int64, "NUMBER(20,0)");
Index: src/NHibernate/Driver/OracleDataClientDriver.cs
===================================================================
--- src/NHibernate/Driver/OracleDataClientDriver.cs	(revision 3695)
+++ src/NHibernate/Driver/OracleDataClientDriver.cs	(working copy)
@@ -52,13 +52,20 @@
 		/// </remarks>
 		protected override void InitializeParameter(IDbDataParameter dbParam, string name, SqlType sqlType)
 		{
-			// if the parameter coming in contains a boolean then we need to convert it 
-			// to another type since ODP.NET doesn't support DbType.Boolean
-			if (sqlType.DbType == DbType.Boolean)
-			{
-				sqlType = SqlTypeFactory.Int16;
-			}
-			base.InitializeParameter(dbParam, name, sqlType);
+			// if the parameter coming in contains a boolean or guid then we need to convert it 
+			// to another type since ODP.NET doesn't support DbType.Boolean or DbType.Guid
+            switch (sqlType.DbType)
+            {
+                case (DbType.Boolean):
+                    sqlType = SqlTypeFactory.Int16;
+                    break;
+
+                case (DbType.Guid):
+                    sqlType = SqlTypeFactory.GetBinary(16);
+                    break;
+            }
+
+		    base.InitializeParameter(dbParam, name, sqlType);
 		}
 
 		#region IEmbeddedBatcherFactoryProvider Members
Index: src/NHibernate/Type/GuidType.cs
===================================================================
--- src/NHibernate/Type/GuidType.cs	(revision 3695)
+++ src/NHibernate/Type/GuidType.cs	(working copy)
@@ -28,10 +28,9 @@
             {
                 return rs.GetGuid(index);
             }
-            else
-            {
-                return new Guid(Convert.ToString(rs[index]));
-            }
+
+            return (rs.GetFieldType(index) == typeof(byte[])) ?
+                new Guid((byte[])rs[index]) : new Guid(Convert.ToString(rs[index]));
 		}
 
 		/// <summary>
@@ -53,7 +52,9 @@
 
 		public override void Set(IDbCommand cmd, object value, int index)
 		{
-			((IDataParameter)cmd.Parameters[index]).Value = value;
+            ((IDataParameter)cmd.Parameters[index]).Value =
+                (((IDbDataParameter)cmd.Parameters[index]).DbType == DbType.Binary) ?
+                    new Guid(value.ToString()).ToByteArray() : value;
 		}
 
 		/// <summary></summary>