MemoryStream m = new MemoryStream();

            XmlTextWriter tw = new XmlTextWriter(m, Encoding.UTF8);

            tw.Formatting = Formatting.Indented;

            tw.Indentation = 4;

            tw.IndentChar = " ".ToCharArray()[0];

            s.WriteObject(tw, p);

            tw.Flush();

            m.Position = 0;

            StreamReader sr = new StreamReader(m);

            string strOutput = sr.ReadToEnd();

            Debug.WriteLine(strOutput);

<Person xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.datacontract.org/2004/07/DomainModel">

    <FirstName>Ruurd</FirstName>

    <LastName>Boeke</LastName>

    <Orders>

        <Order>

            <Amount>5</Amount>

            <ProductID>10</ProductID>

        </Order>

        <Order>

            <Amount>12</Amount>

            <ProductID>11</ProductID>

        </Order>

        <Order>

            <Amount>2</Amount>

            <ProductID>1</ProductID>

        </Order>

    </Orders>