This study investigates the differential effects of two learning contexts, formal instruction (FI) at home and a study abroad period (SA), on the oral production skills of advanced-level Catalan-Spanish undergraduate learners of English. Speech samples elicited through an interview at three data collection times over a 2-year period were quantitatively assessed for fluency, accuracy, and complexity. The results reveal robust fluency gains during SA, moderate improvement in accuracy, and lack of gains in complexity. No gains were obtained during FI. Initial fluency scores, rather than post-FI scores, accounted for a substantial amount of variance in the fluency scores after SA. These findings provide strong evidence for the positive impact of an SA period on the development of oral fluency. (Contains 4 figures, 4 footnotes and 12 tables.)