Yahoo, Microsoft and AOL have teamed up in a fight against Google for ad revenue, entering into a long-expected agreement to sell one another’s ads.

The companies announced the partnership on Tuesday, saying that they will sell ads that don’t normally appear in the most prominent locations and normally go to other ad networks to be sold.

The companies said that the new deal will “reduce friction” in the ad space, saying that it will benefit both advertisers and publishers. On a conference call, the companies said that the effort would start in January.

In its latest earnings call last month, Google reported that it had gained momentum in selling display ads, signing over $600 million worth with agencies and companies, the Wall Street Journal reported. Facebook has also emerged as a giant in the display ad space.

On the call, Rik van der Kooi, vice president of Microsoft Advertising Business Group said that the deal wasn’t “in reaction to anyone in particular” and that the partnership was open to other companies.

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