According to a report published at The Information by senior tech Amir Efrati, Google is at risk of losing precious mobile advertising to Facebook.

Google generates more than twice as much revenue as Facebook in regards to mobile advertising — thanks to search — however, in terms of graphical and video ads viewed on mobile devices, Facebook comes out on top, generating three times as much revenue than Google. In fact, Google’s share of these ads is decreasing.

The inability to track the efficacy of ads across various mobile devices seems to be Google’s greatest hurdle, meaning it’s difficult for Google to prove a sale was made due to a user seeing on its mobile advertisements.

On the other hand, Facebook’s mobile advertising platform seems to be more comprehensive, since it is able to determine if a user views an app on Facebook’s mobile ad and purchases that product on their laptop because of it. Facebook uses cookies — indicators that link a user’s web browser to their smartphone — to gather data about its users.

This is unsurprisingly, considering an estimated 50% of mobile phone owners use their smartphone as their primary internet source.

While Google also collects cookies, it fails to distribute them across its ad products. Data from Google’s search engine isn’t combined with data from Google DoubleClick, which is used to track Google’s ads on non-Google sites. On top of that, Google also has no way of determining whether or not a user has purchased the product they’re already seeing an ad for.

Google seems to be leery of getting flack for using the information they collect on users. The company’s own employees have said that limited ad tracking is a direct result of concerns with government regulations. Though the choice to not integrate Google’s ad products may have been made by its executive some time ago, the exact reasons have not been made clear.