The aim of this article to understand why informal agreements of the hybrid type persist in relations involving the producer and the processor in the raw milk transaction. To address this issue we used the theoretical framework of New Institutional Economics, Transaction Costs Economics and Measurement Costs Theory. Empirically, the study was qualitative, descriptive, inductive with transversal cross-section, the field research was conducted in Paraná, through semi-structured interviews. For analysis of the information obtained was used the Content Analysis Method. The result enabled us to understand the institutional environment, distinguish the categories of technification of producers and analyze the efficiency of hybrid governance. In this discussion, we can identify efficiency in formal contracts with protection indication of the legal rights, minimizing transaction costs and maximizing the value of assets. However, it was found that the informal agreement prevails in hybrid relations. These agreements have efficiency gaps that generate uncertainty, raise transaction costs and limited investments. However, these forms of agreement persist due to the influence of rules the institutional environment and factors such as trust and reputation among the parties.