Sorry, my previous post seems not to be so clear.
Here is what I am confused about:

When you issue the command: ALTER SYSTEM KILL SESSION '13, 8';
The statement kills the session with SID 13 and SERIAL# 8

When you issue the command: ALTER SYSTEM DISCONNECT SESSION '13, 8' POST_TRANSACTION;
The statement disconnects the session with SID 13 and SERIAL# 8

Not much of a difference, isn't it?

I know that the later waits for the transaction to finish before disconnecting the user but the document (http://download-west.oracle.com/doc..._23.htm#2053604) didn't tell us that, did it?

Now what I'm confused about is the 'IMMEDIATE' clause when used with 'DISCONNECT SESSION' and 'KILL SESSION'. Or maybe there is no difference but I just want to know.

Thanks for your reply