The impressive success of peer production – a large-scale collaborative model of production primarily based on voluntary contributions – is difficult to explain through the assumptions of standard economic theory. The aim of this paper is to study the prosocial foundations of cooperation in this new peer production economy. We provide the first field test of existing economic theories of prosocial motives for contributing to real world public goods. We use an online experiment coupled with observational data to elicit social preferences within a diverse sample of 850 Wikipedia contributors, and seek to use to those measures to predict subjects’ field contributions to the Wikipedia project. We find that subjects’ field contributions to Wikipedia are strongly related to their level of reciprocity in a conditional Public Goods game and in a Trust game and to their revealed preference for social image within the Wikipedia community, but not to their level of altruism either in a standard or in a directed Dictator game. Our results have important theoretical and practical implications, as we show that reciprocity and social image are both strong motives for sustaining cooperation in peer production environments, while altruism is not.