We have the same problem with JBoss 3.2.3 and Oracle 9i as persistence mechanism for JMS.
The number of connections and the number of OIL Worker and OILClientILService threads are steadily increasing.
1) You should be using the UIL2 connection factory for external client connections. OIL and OIL2, etc., may deadlock your application.
2) You should use java:/ConnectionFactory for all in-VM connections.
3) You should verify you are properly closing the connection when done.