SQL to find Oracle Database locks

column blocker format a25
column blockee format a25
column sid_serial format a10

select
(select username || ' - ' || osuser from v$session where sid=a.sid) blocker,
a.sid || ', ' ||
(select serial# from v$session where sid=a.sid) sid_serial,
' is blocking ',
(select username || ' - ' || osuser from v$session where sid=b.sid) blockee,
b.sid || ', ' ||
(select serial# from v$session where sid=b.sid) sid_serial
from v$lock a, v$lock b
where a.block = 1
and b.request > 0
and a.id1 = b.id1
and a.id2 = b.id2;