You mean listener.ora doesn't have SID_LIST_LISTENER defined? Hmmm, that is quiet wierd!! Did you do any migration or so?

Though it is said that instances do register automatically to the listener, you first need the listeners started! Do a search and make sure that they are there?

When you do

lsnrctl status

on header you can notice it to point to the parameter file path to the listener.ora file. Check it out...

Sam