How to detect the session who locks other sessions?

I have multiple dbms jobs running and end users are modifying data at the same time. Sometime it looks like a session is locking some other sessions. Does someone have a sql statement to determin which session is locking the others?

Thanks,

YM

run ?/rdbms/admin/catblock.sql
and then you can select from
DBA_DML_LOCKS;
DBA_DDL_LOCKS;
DBA_BLOCKERS;

steve

Run the catblock utlity and then look at the tables dba_locks and dba_blockers.

I also use ...

select a.object_id,a.object_name,b.sid,b.serial#,b.username,c.os_user_name,c.locked_mode
from dba_objects a,v$session b,v$locked_object c
where a.object_id=c.object_id and
b.sid=c.session_id
/

Thank you all very very much