Google is rolling out a dramatic change that removes ads from the right side of its desktop search results, and places ads only at the top and/or bottom of the page. At the same time, the company says it may show an additional ad — four, not three — above the search results for what it calls “highly commercial queries.”

All of this represents the conclusion of a test that began all the way back in 2010, and has been tweaked over the years since then. Search Engine Land readers — particularly some outside the U.S. — notified us late last year that they were seeing the top-only ads more frequently.

A Google spokesperson has confirmed to Search Engine Land that the change is now rolling out to all searches in all languages worldwide. Ads will not appear on the right side of desktop search results, with one exception: Product Listing Ad (PLA) boxes will continue to show both above and to the right of search results.

The additional fourth ad that may show above the search results will only show up for highly commercial queries, according to Google’s official statement on the change:

“We’ve been testing this layout for a long time, so some people might see it on a very small number of commercial queries. We’ll continue to make tweaks, but this is designed for highly commercial queries where the layout is able to provide more relevant results for people searching and better performance for advertisers.”

To clarify, the elimination of right-side ads impacts all desktop searches worldwide; the addition of the fourth ad above search results will happen for “highly commercial queries.” This would involve searches like “hotels in New York City” or “car insurance” and the like.

The removal of all right-side ads obviously makes the desktop and mobile search results more similar. On mobile, though, Google typically shows either two or three ads at the top of the search results.