While previous studies have investigated the acquisition of Spanish vowels by English speakers, none has examined how sequences of vowels are acquired. This study considers the developmental path of acquisition of diphthongs and hiatus by English-speaking learners of Spanish. Previous studies have found that duration is a robust acoustic cue to the difference between a diphthong and a hiatus (Face & Alvord 2004, Hualde & Prieto 2002. This study investigates how the durational difference is manifest in the speech of L2 learners of Spanish and how its realization changes as a function of proficiency in Spanish. In addition, transfer of a phonological constraint in English barring homorganic consonant-glide (CG) onset clusters (Davis & Hammond 1995, Ohala & Kawasaki-Fukumori 1997 and phonetic transfer of the relative intensity values of English glides, which have been found to be lower in English (MacLeod 2008), onto production of Spanish glides are also investigated. A delayed-repetition task with English and Spanish tokens tested 4 groups of speakers: beginning learners, intermediate learners, native Spanish speakers, and native English speakers. The results show that the learners produce a durational difference similar to the native speakers (in that hiatus were, on average, longer than diphthongs), but that the duration of the individual vowels was longer in the speech of the learners as compared to the native speakers. Transfer of the phonological constraint against homorganic CG clusters was found to some extent since glides in homorganic CG clusters were marginally statistically significantly longer than those in non-homorganic clusters in the speech of the beginning learners, but not for native Spanish speakers. In contrast, phonetic transfer of the relative intensity norms of English onto Spanish was not found since the learners produced Spanish glides with a higher relative intensity than the native Spanish speakers. The salience of duration and intensity for English speakers are discussed in concert with general articulatory concerns, both of the vocalic sequences themselves and in terms of the surrounding consonants.