Amazon Self-preferencing in the Shadow of the Digital Markets Act

Regulators around the world are discussing, or taking action to limit, self-preferencing by large platforms. This paper explores Amazon's search rankings of its own products as the European Union's Digital Markets Act (DMA) was coming into effect. Using data on over 8 million Amazon search results at 22 Amazon domains in the US, Europe, and elsewhere, I document three things. First, conditional on rudimentary product characteristics, Amazon's own products receive search ranks that are 24 positions better on average throughout the sample period. Second, the Amazon rank differential is large in comparison with the differential for 142 other popular brands. Third, shortly after the EU designated Amazon a “gatekeeper” platform in September 2023, the Amazon rank differential fell from a 30 position advantage to a 20 position advantage, while other major brands' rank positions were unaffected. The changed Amazon search rankings appear in both Europe and other jurisdictions.