I am trying to design .NET Web Service which will be accessed from Oracle BPEL.

The Web Service will take XML data and I have to parse the XML data in web service.

I would like to know which of the following options is better:

       - Passing XML to Web Service as SOAP Attachments
                       OR
       - Passing XML to Web Service as String
                        OR
       - Any other method

The size of XML ranges from 100 to 300 KB. The number of concurrent transactions will be probably around 30.

I would like to know which is best way to implement.

Thanks in advance.

I implemented both ways like passing as XML string and also XMLdocument.

I would suggest to proceed with XMLdocument. Build the document in the application and pass it as an argument. Then parse it at the webservice end.
Please revert if u have any more doubts.