killing a session immediately

To kill a session in oracle, i generally use,

alter system kill session 'sid,serial#';

(where i get sid, serial# by querying v$session. I also get the unix process id from here).

But this many not kill the processes at the unix level. So, i generally kill the process at the unix level too.

I've found on one of the blogs that you can do this at sql itself (without kill -9 ing) by using

alter system disconnect session 'sid,serial#' immediate;