This study investigated 6 weeks of online asynchronous discussions in a graduate-level course involving eleven students. The research purposes of this study were to identify patterns of collaborative knowledge exploration (CKE) and to suggest new analytical dimensions for investigating online discussions. Based upon a unique theoretical framework integrating the concepts of transition community and discourse community, three major dimensions of online asynchronous learning were adopted in the analysis. The first dimension focuses on the various forms of social negotiation in the discourse. The second dimension regards references to various learning resources, while the third is related to the coherence of the resources utilized. Based upon these dimensions and the analysis of the participating students' online asynchronous discussions, this study suggested ten different patterns of CKE representing the cognitive processes of Elaborating, Challenging, Correcting, and Debating. We argue that the proposed analytical framework allows us to interpret the sociocultural and cognitive aspects of students' interactions for online problem-based learning. In addition, the results suggest that the more cognitively demanding the pattern is, the less frequently it occurs. Potential factors contributing to the observed findings are discussed in this study.