This research investigated the process of argument co-construction in 14 cooperative problem-solving groups in an algebra-based, college level, introductory physics course. The results of the research provide a rich description of argument co-construction, which, while predicted in previous literature, had not been systematically described. The research was a qualitative, case-study analysis of each group's discussion of the "physics description" portion of the group's problem solution. In a physics description physics concepts and principles are use to qualitatively analyze the problem. Transcripts were made from videotapes and the analysis focused on sequential groups of statements, called episodes, instead of isolated, individual statements. The groups' episodes were analyzed and described in terms of Stephen Toulmin's argument structure which consists of claims, grounds, warrants, and backings.