In this study, we examine the interactions among cooperation and five other factors that affect supply chain performance in the context of third party logistics services. We develop a new research model, with degree of cooperation as a mediating construct and test the model’s six research hypotheses using structural equation modelling. The data are from 105 manufacturing firms in Taiwan. The results show that the major factors contributing to cooperation are, in order of importance, self-control costs, transaction frequency and external uncertainty. The findings demonstrate that supply chain members should reinforce their collaborative behavior and activities and enhance cooperation in supply chains to achieve higher levels of performance overall in third party logistics services.