The study investigated the interaction patterns of six ASEAN EFL university students when they worked in small groups on two collaborative writing tasks: a descriptive essay and an argumentative essay. Both groups were homogeneous in terms of gender and heterogeneous in terms of home countries. Data collection included pre- and posttest writing, pre- and post-task questionnaires, participants' work on essays, their reflections, observations, and semi-structured interviews. The students worked on their essays in Google Docs, and the researcher(s) used DocuViz as a tool for visualizations of students' collaborative writing contributions and styles. The findings showed different interaction patterns (a cooperative revision style for Group A vs. a main writer style for Group B) across the two collaborative writing tasks. While revising, both groups added and corrected their essays and employed almost the same writing change functions and language functions, which were suggesting, agreeing, and stating.