Facebook is trying a new design for ads in the desktop News Feed, grouping ads for three different pages into one horizontal “Pages You Might Like” unit.

The new format, which began rolling out over the weekend, helps Facebook fit more ads in the feed without taking up much space. The three-in-one unit is similar to what Facebook has been doing in the mobile feed since August 2012. Now the ads in the mobile module will appear on desktop simultaneously. The ads here are mostly Sponsored Stories, which mean a user has a friend connected to the page, but non-social ads seem to occasionally appear in the unit as well.

To increase revenue, Facebook needs to move more of its ad inventory from the desktop sidebar to the feed. Feed-based ads have higher clickthroughs and generate more revenue per impression. The social network can put a lot more ads in the sidebar, but these are not as effective for advertisers and they don’t translate to mobile. However, ads in the feed can be more interruptive for users, and the balance for Facebook is a delicate one. Creating ad types that are useful and even enjoyable is going to be necessary as more paid content is being slipped between the posts from people and pages that users want to see.

Facebook also began testing a “Games your friends are playing” module in the desktop feed this weekend. The design is similar to “Pages You Might Like” but the example we saw did not include any paid suggestions. We have not heard back from Facebook whether this module will include ads. [Update 1/28/13 11 a.m. -  Facebook tells us this unit is not currently eligible for advertising. Apps that are included in App Center and have App Center screenshots can appear in this module organically.]