Help in writing a piece of .htacess code

Hello,

I am trying to write a piece of .htaccess code to append .php to the end of a URL.

Example:
URL I would like to type in is http://www.xxx.com/subdirectory/fred

it calls up the code http://www.xxx.com/subdirectory/fred.php

I'm trying to solve it with .htaccess so I'm hoping a Guru maybe able to help me please?

Thanks in Advance