Facebook is testing a new type of ad unit called “Related Adverts” that that targets users based on the words they use in their status updates and wall posts, the company has confirmed with us. Though currently only appearing to a very small audience, if this service became publicly available it could create a wealth of new targeting options for advertisers on Facebook.

A new sidebar module called “Related Stories” that shows relevant posts from friends based on the content of a user’s wall posts has also been introduced. This module, though not connected to “Related adverts,” could suggest compelling content for users to discuss with their friends.

Currently, Facebook’s self-serve ad tool only allows advertisers to target based on demographic characteristics, such as their age, gender, education level and the Pages that they Like. Advertisers have not been able to create their own ads targeted based on the words users write in their status updates or wall posts.

Facebook has been testing other new ad designs recently, including one that ask users which they prefer of the displayed ad set. It also recently released a new ad unit called Sponsored Stories that convert news feed posts by users into ads shown to their friends, and began allowing ads to point to a specific tab of a Page. For an in-depth walk-through and strategies for to drive the maximimum number of clicks and return on investment from these ads, visit the Facebook Marketing Bible, Inside Network’s complete guide to marketing and advertising on Facebook.

While this Related adverts test is only appearing to small number of users, and it could be quickly scrapped, the potential for new targeting parameters should excite advertisers. This type of data could help them serve ads based on what a user is currently thinking and posting about, and therefore might be interested in purchasing. This could close the historical gap between advertising on social networks where opinions are formed, and search engines, where users go directly before making a purchase, which is seen as closer to conversion and therefore more valuable in some cases.

Though the data would likely only be available in anonymous, aggregate form, some users may wish to opt out. A minority of users already leave their profile’s demographic information blank to reduce Facebook’s ability to target them. If Facebook decides to expand the test it will need to be careful in how it decides to frames the data usage to users and what, if any, opt out options it will provide. Otherwise, it could see users trying to convince their friends not to post status updates or wall posts

Years ago, Facebook offered a public tool called Lexicon that compared the frequency of words contained in wall posts from across the total Facebook population. Facebook took this powerful keyword analyzer down, leaving a note that it might return in a new form. Maybe this new ad unit is it.

[Thanks to Paul Miller for the tip]