Vocalic mergers affect the set of sounds available in any given dialect, but full phonological analyses of dialects are usually missing, perhaps as a result of the variability observed and the difficulties involved in any categorization. Thus, pointing out distributional facts, like the homophonies between certain vowels, will bring us closer to a systemic perspective.

A number of mergers affect what may be regarded as corresponding pairs of tense and lax vowels. KIT and FLEECE are mostly kept distinct (except in SurC) but may collapse in WMwE, CajE, JamE, and the T&TCs, and before laterals also in innovative urban varieties of SAmE. Similarly, homophony of FOOT and GOOSE is extremely rare, found occasionally in WMwE and TobC and regularly in SurC only; before laterals this merger is spreading in urban SAmE, however. The merger of LOT and THOUGHT, on the other hand, has been widely observed to be spreading in North American English; it is reported for WMwE, CanE, NfldE, CajE and ChcE and occurs conditionally also in NEngE, SAmE, AAVE, and T&TCs. The SurCs also have the merger of these vowels, but their phonetic realization is quite different, a low front [a]. The speech of St. Louis exhibits a characteristically local merger, of the NORTH and START vowels.

TRAP and BATH are pronounced identically practically everywhere with the exception of Jamaica and, with restrictions, T&TCs. TRAP and DRESS may merge before a lateral consonant in Nfl dE, BahE, and CajE. The so-called pin/pen-merger, i.e. homophony of KIT and DRESS before nasals, is a hallmark of SAmE, including CajE, and a conditioned possibility in WMwE, ChcE, InlNE, Nfl dE, and BahE; however, it is said to be recessive in urban centers of SAmE today. DRESS and FACE are distinct, except possibly for parts of WMwE (and SurC). Mergers of mid-front vowels before /r/ have been widely observed in North American English and frequently discussed in the dialectological literature; to some extent they seem to be lexically conditioned. Mary and merry are homophonous in WMwE, InlNE, CanE, SAmE (where the two words were kept distinct until late into the nineteenth century), Nfl dE, Gullah, AAVE, CajE, and ChcE, possibly so also in NYCE, NEngE, BahE and the T&TCs. The homophony of these vowels also includes marry in WMwE, InlNE, SAmE (a recent extension of the previous merger, spreading from urban contexts), AAVE, and ChcE, and potentially a few other dialects as well.

LOT and STRUT are pronounced identically in JamE and possibly the T&TCs but not elsewhere. NEAR and SQUARE fall together in much of the Caribbean (JamE/C, T&TCs), and, with restrictions, SAmE and NfldE.

Vowel nasalization before nasal consonants is the norm almost everywhere. Mutual assimilation phenomena between vowels in the same words occur regularly in Saramaccan, JamC and ChcE, and are possible in SAmE, NfldE and T&TCs. Spelling pronunciation of weak vowels is common in JamC and possible in other Caribbean varieties (T&TCs, BahE) and AAVE.