SQL> create table t (id integer constraint t_pk primary key, val varchar2(100));

Table created.

SQL> -- session 1
SQL> begin
  2    dbms_output.put_line(systimestamp||' session 1: inserting 1');
  3    insert into t values (1,'session 1');
  4    dbms_output.put_line(systimestamp||' session 1: 1 inserted - wait 10 seconds');
  5    dbms_lock.sleep (10);
  6    dbms_output.put_line(systimestamp||' session 1: inserting 2');
  7    insert into t values (2,'session 1');
  8    dbms_output.put_line(systimestamp||' session 1: 2 inserted - end');
  9  end;
 10  /
02/02/2008 19:41:01.453 +01:00 session 1: inserting 1
02/02/2008 19:41:01.453 +01:00 session 1: 1 inserted - wait 10 seconds
02/02/2008 19:41:11.453 +01:00 session 1: inserting 2
begin
*
ERROR at line 1:
ORA-00060: deadlock detected while waiting for resource
ORA-06512: at line 7

SQL> -- session 2
SQL> begin
  2    dbms_output.put_line(systimestamp||' session 2: inserting 2');
  3    insert into t values (2,'session 2');
  4    dbms_output.put_line(systimestamp||' session 2: 2 inserted - wait 10 seconds');
  5    dbms_lock.sleep (10);
  6    dbms_output.put_line(systimestamp||' session 2: inserting 1');
  7    insert into t values (1,'session 2');
  8    dbms_output.put_line(systimestamp||' session 2: 1 inserted - end');
  9  end;
 10  /
02/02/2008 19:41:09.406 +01:00 session 2: inserting 2
02/02/2008 19:41:09.406 +01:00 session 2: 2 inserted - wait 10 seconds
02/02/2008 19:41:19.406 +01:00 session 2: inserting 1
02/02/2008 19:41:23.828 +01:00 session 2: 1 inserted - end

PL/SQL procedure successfully completed.