The present study explores the influence of individual differences in experience, perceptual acuity, and working memory on the development of both declarative and automatized aspects of L2 phonological vocabulary knowledge. A total of 486 Japanese English-as-a-foreign-language (EFL) students took part in two vocabulary tests designed to measure declarative (meaning recognition) and automatized knowledge (lexicosemantic judgement task). Their performance was tied to the quantity and quality of their EFL experience, as well as their scores in auditory processing and working memory. While several significant, modest correlations between experience, aptitude, and vocabulary outcomes were observed, certain predictor variables were uniquely associated with either declarative or automatized vocabulary performance. Specifically, individuals with more extensive, typically language-focused EFL training and greater working memory demonstrated higher levels of declarative knowledge. Conversely, those who pursued extracurricular practice outside the classroom – exposing themselves to auditory materials and/or participating in study-abroad experiences – showed a more automatic execution of vocabulary knowledge.