Reports and arguments supporting positive effects of ER tend to highlight gains in reading speed, but the research base on how reading speed improves among L2 readers, both in general and among those that undergo ER activities, is still limited. This presentation reports on an explorative efforts to identify reader variables associated with reading speed gains among participants in an EFL reading course at a Japanese university (n=24). The two-semester course aimed to improve the students’ reading speed and other skills, and utilised an online ER platform, which recorded student access and activity logs and, among other things, produced reading speed estimates for each e-book they completed reading. Employing a data-mining approach, the presenter compared the students’ reading speeds at the outset and end of the course, and looked for variables linked to speed gains. Findings and their implications are shared at the presentation.