Changing isolation level?

Folks,

  I have been working with DB2 for few years now, and in DB2 I can use the   isolation level of CS. If one process has updated the row or deleted the row   but not yet commited it, and another process tries to read it, it will be   blocked until the first process commits the changes.

  In Oracle the default behaviour is that the select of the second process   gets the old version of the data. How can I change the isolation level,   preferably at database level, so that is blocks the selects if the select   for update and delete has not yet commited the changes.   

  Which isolation level in Oracle can I use?

-- 
Hemant Shah                           /"\  ASCII ribbon campaign
E-mail: NoJunkMailshah_at_xnet.com       \ /  --------------------- 
                                       X     against HTML mail
TO REPLY, REMOVE NoJunkMail           / \      and postings      
FROM MY E-MAIL ADDRESS.           
-----------------[DO NOT SEND UNSOLICITED BULK E-MAIL]------------------
I haven't lost my mind,                Above opinions are mine only.
it's backed up on tape somewhere.      Others can have their own.