the following document [url]http://technet.oracle.com/docs/products/oracle8i/doc_library/817_doc/server.817/a85397/statem2a.htm#2056065
states:
You can free only unused space above the high water mark (that is, the point beyond which database blocks have not yet been formatted to receive data).
I always had an impression that deallocated unused will free up a space below hight water mark.
According to the document located at the link above 'deallocate unused' does not re-gain anything below the hight water mark...
Please help me to understand this issue...