This is how I think the tx behaviour should be: 1) CMT, tx=NOT_SUPPORTED, local_optimisation = false: MDB should be *non transacted* - it should use the ack mode as specified in the meta data 2) CMT, tx=NOT_SUPPORTED, local_optimisation = true MDB should be *non transacted* - it should use the ack mode as specified in the meta data 3) CMT, REQUIRED, local_optimisation = false: MDB should create a JTA tx *before delivery* and commit at completion of onMessage 4) CMT, REQUIRED, local_optimisation = true MDB should create a *** local tx *** *before delivery* and commit at completion of onMessage 5) BMT, local_optimisation = false: MDB should be *non transacted* - it should use the ack mode as specified in the meta data (unless a user transaction is started) 6) BMT, local_optimisation = true MDB should be *non transacted* - it should use the ack mode as specified in the meta data (unless a user transaction is started) View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4244925#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...