Hi,
it appears "idleConnectionTestPeriod" is missing, also you should select an appropriate connection testing strategy.
You'll find all details well explained in the docs included in the c3p0 package:
http://sourceforge.net/project/showfiles.php?group_id=25357
Also the docs contain some more suggestions for Oracle.
BTW this is meant for a standalone app right?
When deploying in an application server as JBoss you don't need to use c3p0 and can enable very smart behavior just setting some options in the datasource definition.