List blocking sessions

Below is a query that list all the blocking sessions in an oracle instance

WITH sessions AS
       (SELECT username,sid,sql_id
          FROM gv$session),
     locks AS
        (SELECT * FROM gv$lock)
SELECT l2.type,s1.username blocking_user, s1.sid blocking_sid,
        s2.username blocked_user, s2.sid blocked_sid, sq.sql_text
  FROM locks l1
  JOIN locks l2 USING (id1, id2)
  JOIN sessions s1 ON (s1.sid = l1.sid)
  JOIN sessions s2 ON (s2.sid = l2.sid)
  LEFT OUTER JOIN  v$sql sq
       ON (sq.sql_id = s2.sql_id)
 WHERE l1.BLOCK = 1 AND l2.request &gt; 0;