This study investigates the knowledge flows among and between project managers and project management office (PMO) members in a pharmaceutical R&D company in China, using a mixed-methods approach. The results show that knowledge exchange happens in clusters, where each cluster forms around a PMO member. Contrary to expectations, PMO members were not identified as the most popular knowledge providers in these clusters; instead, knowledge was requested from earlier collaborators. A three-tiered model is developed for knowledge governance at the cluster level, across clusters and the link with corporate and project governance structures. Managerial and theoretical implications are discussed.