Amazon's ad revenue is the same as Twitter and Snap combined

"Advertising is still just a small piece of Amazon’s growing empire. But “small” is relative. In 2017, the company’s ad business generated $2.8 billion, making it bigger than the ad platforms managed by Twitter ($2 billion) and Snap ($800 million). Only three online ad platforms outrank Amazon’s: Google, Facebook, and Oath.
The bulk of Amazon’s ad revenue is generated by placements within Amazon.com. For example, sellers pay to appear in search results, or display custom banners above the results. Some, like toy company Melissa & Doug, shell out additional dollars for custom Amazon home pages. But the retail conglomerate has also started to explore ad placements across the wider web, as well as within Alexa and Prime Video. Marketers, drawn by Amazon’s wealth of shopper data, have been eager to experiment. Last spring, WPP acquired an Amazon-focused consultancy."

Source:  FastCompany, 29th January 2018