Storage Space consumption by user account (Oracle 10g)

Select
      owner,
      round((byte_count / 1024 /1024 ), 2) space_used_MB,
      round(100 * (byte_count / tot_bytes) , 2) pct_of_database
from
    (select
            owner,
            sum(bytes) as byte_count
      from
            sys.dba_segments
      where
            segment_type not in ('TEMPORARY', 'CACHE')
      group by owner
      order by 2 desc),
        ( select sum(bytes) as tot_bytes
          from sys.dba_segments);


IF users account found with large amount of data, user should checked is there unused or unnecessary objects have not been left.

Temporary space used by connected sessions (oracle 10g)
Temporary space used by SQL call in current session (oracle 10g)