Google has extended invitations to mobile website publishers to test the display of AdSense ads on those sites, reports PC World.

The search/advertising giant is conducting a limited test of the system as it gathers feedback for use in developing a final product. Getting AdSense into the mobile world would be a major coup for Google, as more and more users fire up their wireless devices for web surfing purposes.

In order to participate, sites must be written in one of three mobile-friendly markup languages. The restrictions are due to Google's crawlers needing to be able to read the page in order to place appropriate ads.