The actress -- who's made out with Penelope Cruz and Christina Ricci before for work -- went girl-on-girl again yesterday after offering up her lips for the OneXOne celebrity auction in San Francisco.

The result: A steamy, 25 second smoochfest with the mystery woman who paid top dollar.

Read more: http://www.tmz.com/2009/10/23/charlize-theron-girl-on-girl-kiss-charity-auction-video/#ixzz0UnJgPOMk