The Eu General Data Protection Regulation has introduced a new «right to data portability ». While the provision has the main purpose of strengthening individual rights, it constitutes at the same time a legal instrument that could facilitate competition in the digital markets. As a consequence of the broad construal of the concept of «personal data» in Eu law, the right to data portability applies as a matter of fact to a wide range of datasets, thereby overlapping with a number of conflicting rights and interests that subsists in those datasets. This raises the issue of how to balance conflicting interests and to secure efficacy to data portability as a market regulatory instrument. The article shows that such efficacy largely depends on the structure of the relevant market. It argues that the pro-competitive effect of data portability is more pronounced in markets that adopt interoperable standards. By contrast, the effect is largely uncertain in absence of commonly shared standards of data processing.