Google is officially rolling out what could be a solid new revenue stream

Google is officially rolling out search ads on its Google Play app store, after beta-launching with only a few customers in February.

Now, when users search for something like "mileage tracker" or "restaurant," they'll start noticing sponsored results that a developer paid for.

Selling ads on Google Play is a big opportunity for Google.

It makes sense: The company makes billions of dollars a year from search advertising on web search and YouTube - adding Google Play just sweetens the pot and adds another avenue for mobile monetization.

Google Play search ads could provide a big revenue boost to Google.

Along with the search ads, Google is also launching a new way for advertisers to track their return on investment.

With "Android first app opens," Google will measure when a user first opens an app after clicking on an ad and completing an Android app install. If the company proves that people are actually using the apps downloaded because of its new Play Store ads, Google will be able to make more money from them. The tool will be available for all of Google's app promotion ads, across YouTube, the Google Display Network, and AdMob.

Mobile app install ads have continued to rise in popularity, with BI Intelligence data showing that US mobile app-install ad revenue will top $4.6 billion this year and grow to $6.8 billion by the end of 2019. The format has been incredibly lucrative for Facebook in particular: They cost more than three times as much as the average Facebook ad.

"Search Ads on Google Play can provide consumers new ways to discover apps that they otherwise might have missed and help developers drive more awareness of their apps," Google said in its blog post announcing the news.

Business Insider talked to a bunch of developers back when Google first introduced the format, and reactions ranged from excitement, to the feeling that it would make the strong stronger, and the weak weaker, with small dev houses unable to afford the new ads seeing their search results buried under an influx of paid results.

However, in all of Google's examples, there seems to be only one ad shown per search.

Apple doesn't yet offer search ads in its App Store, but it will be interesting to see if Google's roll-out nudges it in that direction.