The Bulaesti Ukrainian dialect is characterized by the complete absence of a prosthesis /w/ before /u/. Thus, we see Bulaestian /|удул/ ‘hoopoe’, /у|жеука/ rope made of twigs’, /|уйко/ ‘uncle; great-grandfather‘. Also, the prosthesis /w/ before /o/ is very characteristic for Bulaestian dialect. These facts arise the issue of the chronological sequence of the mentioned variants of prosthesis in the Ukrainian (Carpathian-Ukrainian) dialects. The reason is that to a certain extent, a paradoxical picture is observed. The closely related (and, obviously, ancestral) to Bulaestian dialect in lexica and phonetics, Bukovinian and Hutsul dialects, on the contrary, are characterized by the opposite ratio: a wide, almost ubiquitous spread of prostheses /v/ before / u/, and a very uneven spread (with a tendency to complete absence) of prostheses /v/ before /o/. So, it is obvious that by the time of the development of the processes associated with the prosthesis in the Hutsul and Bukovina dialects, the Bulaeshti dialect was largely isolated from them, caused, presumably, by a more or less significant territorial (or territorial-political) barrier that already existed between them at that time.