•Intrusive vowels in Sgi Bara are significantly shorter than phonemic vowels.•They are also more peripheral in the vowel space.•They don’t differ in intensity.•The differences between intrusive and phonemic vowels help us solve certain phonological problems. We provide a phonetic examination of intrusive vowels in Sgi Bara jil. These vowels are inserted in predictable places, and their quality (either i, ɨ, or u) is also predictable, so they are not considered phonemic. We demonstrate that they differ from phonemic vowels in their duration, being shorter; and in their articulation, being more peripheral; but not in their intensity. We then demonstrate how this phonetic understanding of the difference between intrusive and phonemic vowels can be used to answer phonological questions about Sgi Bara. We offer two case studies: phonologically ambiguous sequences of high vowels, and frequent two-word combinations that may be univerbating. The results confirm the existence of a distinction between intrusive and phonemic vowels.