Cross-sector co-production involving voluntary organisations in the production and delivery of social services has been adopted across many welfare states. Economic and demographic changes have led to increased involvement of volunteer initiatives in different welfare policy fields. How different field properties enable, constrain, and shape co-production practices remains, however, under researched. In this article, we address this shortcoming in a comparative case design exploring the practices of co-production within the two fields of elderly services and refugee services. We develop a conceptual framework and demonstrate that differential distribution of resources leads to diverging outcomes and perspectives for co-production. Based on a two-year in-depth study of one large Danish municipality, we find two forms of co-production practices, which reflect different field conditions. In the field of elderly services, co-production takes the form of ‘embedded’ practices, and in the field of refugee services co-production takes the form of ‘exterior’ practices. We demonstrate that each of these co-production forms entail ambiguous outcomes and antagonistic positions for voluntary and public sector actors, depending on the policy field.