On the basis of the results found, we argue that the members of the spectrally similar vowel pairs /e-ɪ/, /e-ε/, /ɔ-ʌ/, and /o-ʊ/ (with less than 1 Bark distance between the members) will still be sufficiently distinct in Iranian EFL speech because the members of these pairs differ substantially in duration. However, the duration contrast in the pairs /i-ɪ/ and /u-ʊ/ is rather small, so that some confusion may arise. The strongest confusion will be obtained for the pair /ɑ-ʌ/ whose members are spectrally the same and do not differ in duration.