This study investigates the acoustic characteristics of monophthongs in four Iranian linguistic varieties: standard Persian (Tehrān), Gilaki (Rasht), Lori (Khorramābād), and Kordi (Kermānshāh). Vowel productions were analyzed in both citation-form speech (single words) and continuous speech from 80 speakers (10 speakers per speech style per variety). Acoustic analysis revealed that vowels in continuous speech were more centralized compared to citation-form speech across all varieties, with smaller vowel space areas (VSA). Female speakers consistently produced higher formant frequencies and larger VSA than male speakers across all varieties. In citation-form speech, Persian demonstrated the largest VSA despite having the smallest vowel inventory (six vowels), followed by Lori, Kordi, and Gilaki. This pattern largely persisted in continuous speech for male speakers, while female speakers showed a different ordering (Lori > Persian > Gilaki > Kordi), suggesting that VSA size is not directly correlated with vowel inventory size. These findings contribute to our understanding of acoustic variation in Iranian languages and the relationship between speech style, gender, and vowel space characteristics.