Language immersion students' lexical, syntactic, and pragmatic competencies are well documented, yet their phonological skill has remained relatively unexplored. This study investigates the Spanish vowel productions of a cross-sectional sample of 35 one-way Spanish immersion students. Learner productions were analyzed acoustically and compared to those of Spanish-English bilingual peers. Findings reveal that learners' productions differ from those of their native Spanish-speaking peers on nearly all measures; observed differences may be the result of transfer of first language phonetic and phonological tendencies and the nature of the input received.