Abstract: Many field public goods are provided by a small number of contributors: the “superstars” of their respective communities. This paper focuses on Wikipedia, one of the largest online volunteering platforms. Over 9 consecutive years, we study the relationship between social preferences – reciprocity, altruism, and social image – and field cooperation. Wikipedia editors are quite prosocial on average, and superstars even more so. But while reciprocal and social image preferences strongly relate to contribution quantity among casual editors, only social image concerns continue to predict differences in contribution levels between superstars. In addition, we find that social image driven editors – both casual and superstars – contribute lower quality content on average. Evidence points to a perverse social incentive effect, as quantity is more readily observable than quality on Wikipedia.