This study examines the role of lexical resources in oral language acquisition using a mixed-methods approach at the intermediate and advanced levels of English language learning. Quantitative analysis shows that lexical diversity significantly predicts speaking ability, while vocabulary accounts for changes in overall speaking ability. Learners with extensive lexical resources showed significantly higher fluency and improved task performance than those with limited vocabulary. Qualitative findings show that speakers with rich lexical resources express their ideas more clearly, more effectively bridge communication gaps, and have increased self-confidence. The results confirm that lexical competence is a key element of effective oral communication and have implications for pedagogical approaches that prioritize vocabulary development alongside traditional grammar and pronunciation instruction.

lexical resource, speaking proficiency, vocabulary knowledge, oral communication, lexical diversity, collocations, language fluency.

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