<p>A great deal of the research on cross-linguistic phonetic influence demonstrates that a speaker’s knowledge of their first language (L1) significantly affects their ability to perceive and produce sounds in any other language. While current studies show that cross-linguistic transfer occurs at the L3 level, some research suggests that properties of both L1 and L2 are present in the production of L3 (Ionin, Montrul & Santos, 2011). Many studies have addressed perception, production and factors that influence foreign speech in Second Language Acquisition (SLA) (Watkins, Rauber & Baptista, 2009). As the number of multilingual individuals rises, so does the need for studies that investigate not only SLA but also that of additional languages (i.e., Third Language Acquisition). This dissertation examines how cross-linguistic influence (CLI) occurs among English, Spanish, and Brazilian Portuguese (BP), examining instances of vowel reduction, an aspect of phonological production. English and BP are assumed as vowel reducing languages, whereas Spanish displays negligible vowel reduction in comparison. The vowel productions in L3 BP of two multilingual groups, L1English-L2Spanish-L3BP (ESP) and L1 Spanish-L2 English-BP (SEP) were investigated in two tasks: a paragraph reading task (PRT) and a carrier phrase task (CPT). The study sought to determine whether i) a native speaker of a vowel reducing L1 and a non-vowel reducing L2 displays more or less vowel reduction in a vowel reducing L3 than a native speaker of a non-vowel reducing L1 and vowel reducing L2 and ii) how length of exposure to an L3 affects phonological production. Three fixed effects were considered: duration ratio, intensity ratio and height (F1). The goal was to ascertain whether the Typological Primacy Model (TPM) (Rothman 2011, 2015) or the L2 Status Factor Model (Bardel & Falk 2007, 2012; Hammarberg, 2001) would be a better predictor for how vowel reduction would occur in the L3. Results for duration ratio and vowel height showed no significant difference between groups ESP and SEP. Results for intensity ratio suggest L2 Status as a better predictor, as group SEP displayed more phonological transfer than the ESP group. A hybrid approach to L3 acquisition models is proposed. </p>