Amazon’s ad business is on the rise, and a new eMarketer report estimates its digital ad revenues will more than double this year, vaulting it into third place behind the powerful duopoly of Facebook and Google.

At $4.61 billion in revenue, it is predicted to surpass Oath and Microsoft, accounting for 4.1% of all digital ad spending in the country. The eMarketer report notes that this year’s dramatic growth is partly due to an accounting change Amazon made that affects estimates for 2018 and beyond. Growth has nevertheless also been much stronger than expected.

It isn’t just the tech giants keeping a close eye on Amazon as a large-capacity ad vehicle. As it continues to push into streaming video, including a renewed deal for NFL Thursday Night Football, Amazon is spooking traditional ad-dependent TV networks as well. Only a small sliver of the ad pie for the e-commerce giant comes from video, however, especially since most programs air without commercials.

Instead, the company’s scale enables it to not only sell ads on its own properties but also facilitate ad transactions across the Iinternet.

The eMarketer report predicts increases of more than 50% per year through at least 2020, when Amazon will control 7% of all U.S. digital ad spending.

In the digital realm, no rival can match Facebook and Google, however. Even after the projected growth of Amazon, its share will pale next to Facebook’s 20.8% and Google’s 35.1% of ad dollars.

Earlier this month, Amazon introduced several innovations to its ad efforts, organizing them under a comprehensive, rebranded “Amazon Advertising” umbrella.

Here’s a chart from the eMarketer report:

Duopoly vs. Amazon Share of Total US Digital Ad Spending, 2018 & 2020 (% of total digital ad spending)