My client comes with an Oracle 11g installed and wish migrate the organization site to some Content management systems that utilizes the oracle.

There's an "experimental" Oracle driver module for Drupal. From things i understand, adding support for brand new database backends is simpler in Drupal 7 since it uses PDO. For example, Drupal 7 includes support for SQLite in core.

Used to do some quick searching and did not find anything equivalent for WordPress or Joomla, another two Content management systems packages you incorporated within the tags.

There's this post around the forum for that Fabrik joomla extension extension that describes an area to permit the aspect of connect with an Oracle database. It had been led with a user, and that i personally cannot attest to it, however.