The social networking titan said Friday that it is now testing online ads for the Craigslist-like service, similar to what they would see in Facebook’s core newsfeed.

Currently, only a small percentage of U.S. users will see the ads, which resemble the product listings in Marketplace, said Mike Manning, a Facebook spokesperson about the company’s monetization efforts. The ads are labeled with the advertiser’s name along with the word “sponsored” to distinguish them from other Marketplace postings, he said.

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The ads will only be shown in the mobile version of Facebook and not on the desktop computer version, said Manning.

Facebook (FB) debuted Marketplace in October as a way to expand beyond the company’s primary social networking service. Facebook does not handle transactions via Marketplace, and instead acts as a facilitator between buyers and sellers who handle the transactions and delivery of items themselves.

By testing ads on Marketplace, Facebook is attempting to expand its multi-billion dollar advertising business, which had $7.9 billion in sales in its latest quarter. People posted over 18 million items on Marketplace in May alone, Manning said, which indicates that many people are using the service.

Manning declined to say which third-party advertisers are part of the trial, but he said they currently run advertising campaigns across other Facebook services, like the core service and the photo-sharing app Instagram.

Facebook is not charging advertisers during the test, which is intended to see how successful the ads are. Manning said the test will run for the foreseeable future, and that it’s too early to tell if ads will become a permanent addition to Marketplace.