This article reports on a longitudinal study on the impact of reading mode on incidental collocation learning and predictors of learning gains. The experiment lasted 11 weeks and involved 118 Vietnamese EFL learners who were assigned to an experimental group and a no-treatment control group. The experimental group encountered 32 target collocations in three graded readers in three reading modes: reading-while-listening, reading with textual input enhancement (i.e., underlining), and reading-while-listening plus textual input enhancement in a counterbalanced fashion. Incidental learning was assessed at the level of form recall. The findings indicated a significant effect of reading mode on the learning of collocations. Significantly more collocations were learned in reading-while-listening plus textual input enhancement and reading with textual input enhancement modes than in reading-while-listening mode. Reading-while-listening plus textual input enhancement, however, did not differ significantly from reading with textual input enhancement. The results also revealed that learners' prior vocabulary knowledge and collocational congruency significantly affected learning.