The article provides an overview of vowel quality in the initial syllable of words having various degrees of quantity in the insular dialect of Estonian. The material consists of eight sub-dialects of Saaremaa. The article presents measurement findings of the formant analysis and their discussion. The acoustic-phonetic data served as a basis for establishing the systems of vowels in the sub-dialects of Saaremaa. The results allowed distinguishing 8 vowels (a, o, u, ä, e, ö, i, ü). Length affects vowel quality — overlong mid-high monophthongs are raised. The area under discussion has no unrounded central vowel õ of Standard Estonian; it has developed into a mid-high rounded front vowel, the quality of which is close to the short and long ö but not the overlong ö. The vowels ö and open ö have merged. Only in some words in western Saaremaa ä has developed into a mid-high short or overlong monophthong, the quality of which is close to the short and long e but not the overlong e. The sound ™ is an allophone of e.