Using Oracle 11 g drivers (ojdbc5.jar) with Websphere Application Server 6.1 :
If you change your provider and datasource to use 11g drivers make sure you select the 11g data store helper and make sure the datasource custom property
oracle9iLogTraceLevel is blank, to avoid having the 9i or 10g API called.

You can get the following error otherwise :
java.lang.NoSuchMethodError: oracle/jdbc/driver/OracleLog.setLogVolume

http://www-01.ibm.com/support/docview.wss?rs=180&context=SSEQTP&dc=DB550&uid=swg1PK47930&loc=en_US&cs=UTF-8&lang=en&rss=ct180websphere