Technology-mediated task-based language learning and teaching has long been a research focus (Chapelle, 2001; Gonzalez-Lloret & Ortega, 2014). The focus has mainly been on the task-as-workplan (Ellis, 2003) leaving the process aspect as a research gap (Breen, 1989; Seedhouse, 2005). Therefore, the collaborative and interactional nature of language learning tasks remained largely unexplored or misguided by etic constructs. This study aims to describe the interactional unfolding of online task-oriented collaboration of undergraduate students who are also learners of English as a foreign language (L2). Seven L2 learners have participated on a Google Hangouts video meeting for the study, discussed some clues, and hinted their team mates in order to complete a task collaboratively before the other teams do. The naturally occurring interactions of the participants have been recorded via a screen capture software. A 90-minute long recording has been transcribed and examined using conversation analysis (CA) methodology. As result of a turn-by-turn single case sequential analysis, an emergent recurring pattern has been discovered. It has been found that whenever an unknowing participant's candidate answer is confirmed by a knowing participant, the sequence is expanded and therefore enhanced, and then it functions as an epistemic progression (Gardner, 2007) step which takes the learners to the knowing position through accumulation of knowledge. This finding has showed that the learners close knowledge gaps, construct and accumulate knowledge, and thus accomplish tasks collaboratively through epistemic progression. It has also showed that an investigation into the process aspect of tasks may bring new insights into an understanding of the nature of collaboration occurring in and through online task-oriented interaction. (C) 2015 The Authors. Published by Elsevier Ltd.