Unable to get exact Encoding specified in xmlWriteSettings

I am trying to get xml of an object. To further streamline the xml i have added some settings like indent= true and Enconding.

I have set the encoding to "ISO-8859-1" but when the code get executed oXmlWriter's setting become utf-16 instead of ISO-8859-1" Do anyone have idea why it is behaving so ?

public static string ObjectToXml(object obj)
    {
        var oXmlSerializer = new XmlSerializer(obj.GetType());
        var oStringWriter = new StringWriter();
        var oXmlSerializerNamespaces = new XmlSerializerNamespaces();
        oXmlSerializerNamespaces.Add(string.Empty,string.Empty);
        var oXmlWriterSettings = new XmlWriterSettings
        {
            Indent = true,
            OmitXmlDeclaration = false,
            Encoding = Encoding.GetEncoding("ISO-8859-1")
        };

        var oXmlWriter = XmlWriter.Create(oStringWriter,oXmlWriterSettings);
        oXmlSerializer.Serialize(oXmlWriter, obj, oXmlSerializerNamespaces);
        oXmlWriter.Close();
        return oStringWriter.ToString();
    }