Originally posted by omran
So how can I lock the table while exporting?
I can't imagine why in the world would someone want to lock the table while exporting it, but if you realy need to do it, you simply logon to the database with SQL*Plus (or whatever your favorite tool to interact with Oracle database is) and lock the table using SQL command. Then perform your export in another session and once the export is done, you unlock the table from your first session.

Once again, it would be intesresting to know why would you like to prevent changes to the table while exporting it.