This article aims to investigate how university students perform agency in an online course and whether the collaborative nature of the course affects such expression. A total of 11 online web forums involving 18 students (N = 745 posts in total) were qualitatively analysed through the use of a codebook composed of five categories (individual, interpersonal, epistemic, transformative and collective) and several sub-categories purposely developed for the sake of this research. The results show that each category follows a specific path, although two events--the re-mixing of the groups and the assumption of the peer-tutor role--particularly affected the evolution of trends. Although this study needs further development, the authors believe that an in-depth understanding of the nature of agency, including how to analyse it as well as empower it when implementing blended educational activities, engages relevant theoretical and pedagogical issues.