This research investigates the relationship between social interaction amongst volunteers working for non-profit organizations and their satisfaction with what they are doing. Drawing on the literature on social capital, we apply social network theories so as to represent various kinds of interaction. We then specify a CATREG model to pick up the effects of goal-specific social capital on volunteer satisfaction. We test our hypotheses on a population of 100 volunteers in a non-profit organization. The empirical evidence we collect reports that benefits of co-working relationships, like the opportunity to acquire competences or the involvement in decision making, affect levels of satisfaction more than any outcomes of solidarity interaction.