Today my friend asked me what is the different between kill session and disconnect session. After researching I found useful information and here I`m going to share briefly. Using Disconnect Session clause to disconnect the current session by destroying the dedicated server process. Using Kill Session clause let you mark a session as terminated, release locks. Example: SQL>ALTER SYSTEM DISCONNECT SESSION 'sid,serial#'; SQL>ALTER SYSTEM KILL SESSION 'sid,serial#'; For more details please refer to : http://oracletempspace.wordpress.com/2011/04/20/example-alter-sytem-disconnect-vs-alter-system-kill-for-currently-connected-sessions/