How to Apply the Self-Preferencing Prohibition in the DMA

In the years preceding the adoption of the Digital Markets Act (DMA),1 the issue of self-preferencing has appeared in the context of e-commerce platforms (Amazon), search engines (Google Search and Google Shopping), and mobile app stores (Google and Apple), but it is of broader concern. Self-preferencing can be seen as part of the platform’s design decision, how a platform manages its ecosystem, which includes decisions about the treatment of third-party products and services relative to its own products and services. ... The case against self-preferencing may look clear from an economic theory point of view to the extent that it amounts to unequal treatment of equal offers. As such, several economists have taken the view that self-preferencing should, in general, be prohibited: ‘We would suggest that any form of discrimination against third parties be deemed unlawful. In other words, we believe self-preferencing is a natural candidate for the “blacklist” of practices to be deemed anti-competitive and “per se” disallowed’.2 Such an unequivocal statement from a diverse set of academic economists is quite remarkable.3 In their report to Commissioner Vestager, another group of academics (only one of whom is an economist) are more careful: ‘In a market with particularly high barriers to entry and where the platform serves as an intermediation infrastructure of particular relevance, we propose that, to the extent that the platform performs a regulatory function, it should bear the burden of proving that self-preferencing has no long-run exclusionary effects on product markets’.4