Lists slow SQL in library cache for tuning investigations:
set pages 9999 spool c.lst select elapsed_time/1000000 secs, executions, elapsed_time/1000000/greatest(executions,1) secs_per_exec, sql_text from v$sql where executions > 50 and elapsed_time/1000000/greatest(executions,1) > 1 order by 3 desc / spool off ed c.lst
For older versions of oracle, use buffer_gets or disk_reads in place of elapsed_time.