SELECT *
  FROM (  SELECT sql_text,
                 cpu_time / 1000000 cpu_time,
                 elapsed_time / 1000000 elapsed_time,
                 disk_reads,
                 buffer_gets,
                 rows_processed
            FROM v$sqlarea
        ORDER BY cpu_time DESC, disk_reads DESC)
 WHERE ROWNUM < 21;

SELECT se.username, ss.sid, ROUND (value/100) "CPU Usage"
FROM v$session se, v$sesstat ss, v$statname st
WHERE ss.statistic# = st.statistic#
   AND name LIKE  '%CPU used by this session%'
   AND se.sid = ss.SID 
   AND se.username IS NOT NULL
  ORDER BY value DESC;