To say that “data is the new oil” is already an abused commonplace. What are the implications for justice? In our contribution, we argue that if data is the new oil, the extraction of value from data is unjust if it is achieved by means of dominant internet platforms that are unjust. We define the concept of “dominant internet platforms” and explain why a Rawlsian conception of justice can be argued to apply to them. We argue that dominant internet platforms are fundamental social institutions. We illustrate the implications of Rawlsian principles of justice in this domain, by considering the problem of free speech on existing web platforms (YouTube, Facebook, and Google Search) that are arguably dominant in many western societies.