This study explored how the construction of an argument graph promotes students' collaborative online reading compared to note-taking. Upper secondary school students ("n"?=?76) worked in pairs. The pairs were asked to search for and read source material on the Web for a joint essay and either construct an argument graph or take notes during online reading. The data consist of transcription protocols of student pairs' discussions and joint essays. The study indicated that argument graphs may be useful tools when teachers want students to pay attention to the argumentative content of online sources and to consider relations between arguments. Additionally, with argument graphs, teachers can support students' post-reading activities, such as source-based argumentative writing. (Contains 5 tables and 1 figure.)