The integration in second-order cooperatives allows the first-order agricultural cooperatives to complement their resources and capabilities, achieving a sustainable competitive advantage. The problems associated with the creation, development and long-term maintenance of these partnerships, along with the lack of research into this area, justify the realization of studies aimed at improving our understanding of the processes and outcomes that characterize them. Therefore, the purpose of this study is to discover the factors which lead to the success of these relationships, empirically measured through the satisfaction of first-order co-operatives with the relationship. In order to achieve this, a suitable theoretical framework is established and an empirical study undertaken, with information obtained from a survey of 190 Spanish first-order agricultural co-operatives. The results obtained reveal that the contribution of the partnership to the first-order cooperative's performance, its trust and perception of fairness are critical antecedents of the level of satisfaction of the first-order cooperative satisfaction with the relationship.