How can I detect, using php, if the machine has oracle (oci8 and/or pdo

How can I detect, using php, if the machine has oracle (oci8 and/or pdo_oci) installed?

I'm working on a PHP project where some developers, such as myself, have it installed, but there's little need for the themers to have it. How can I write a quick function to use in the code so that my themers are able to work on the look of the site without having it crash on them?

if the oci extension isn't installed, then you'll get a fatal error with farside.myopenid.com's answer, you can use function_exists('oci_connect') or extension_loaded('oci8') (or whatever the extension's actually called)