I think you're confusing "maxSession" with "maxMessages". "maxSession" controls the number of concurrently operating threads. The pool size controls the number of MDB object instances created and pooled by JBoss. This pool size should be larger than the number of concurrent threads, otherwise the threads get blocked. Anyway, you probably don't need to worry about messing with these settings in EJB3, unless there's some performance issue you're dealing with. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4093655#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...