In this article we investigate whether long-term radioactive waste management by means of geological disposal can be understood as a social experiment. Geological disposal is a rather particular technology in the way it deals with the analytical and ethical complexities implied by the idea of technological innovation as social experimentation, because it is presented as a technology that ultimately functions without human involvement. We argue that, even when the long term function of the ‘social’ is foreseen to be restricted to safeguarding the functioning of the ‘technical’, geological disposal is still a social experiment. In order to better understand this argument and explore how it could be addressed, we elaborate the idea of social experimentation with the notion of co-production and the analytical tools of delegation, prescription and network as developed by actornetwork theory. In doing so we emphasize that geological disposal inherently involves relations between surface and subsurface, between humans and nonhumans, between the social, material and natural realm, and that these relations require recognition and further elaboration. In other words, we argue that geological disposal concurrently is a social and a technical experiment, or better, a long-term socio-technical experiment. We end with proposing the idea of ‘actor-networking’ as a sensitizing concept for future research into what geological disposal as a sociotechnical experiment could look like.