Reduction of unstressed vowels is a well-known aspect of English phonology that is not present in Spanish, and the absence of such reduction contributes to accentedness in English for L1 Spanish speakers (Flege & Bohn, 1989). Previous studies have established that stress, coarticulatory effects of the previous consonant, and sociolinguistic factors can all lead to English vowel reduction in L1 and L2 speakers (Byers & Yavas, 2017). The current study investigates how lexical stress and sociolinguistic factors can affect vowel reduction in 10 American English monolinguals and 10 Spanish-English bilinguals from Colombia. A shadowing task provided acoustic measurements of formant frequencies for 60 target words in Spanish and English, encompassing five vowels from each language and two levels of stress. Factors such as language dominance, age of acquisition, linguistic attitudes, and length of residence were assessed through a questionnaire to examine their respective influences on the degree of vowel reduction shown by bilinguals relative to native monolinguals. Results address the degree of vowel reduction in L1 and L2 English and L1 Spanish, as impacted by linguistic and extra-linguistic factors.