As mentioned above, variation within these speech communities is considerable and surveying the phonetic and phonological features of these languages is extremely difficult on account of varying degrees of interference from local vernaculars and from the lexifier language English. These two influences have a significant effect on the extent and the nature of the vowel inventories that we find here.

As in the case of pidgins and creoles elsewhere, the contact languages in this region show vowel systems that are considerably reduced. This means that there is substantial vowel neutralization and consequently these languages permit much larger numbers of homophones (words that are pronounced the same) than do other varieties of English. Bislama, Solomon Islands Pijin, Tok Pisin (with roots in earlier Melanesian Pidgin), Fiji English and the Australian creoles, Cape York Creole and Kriol, all share a five vowel contrast: /i/, /u/, /e/, /o/, /a/. The phonetic realization of these segments is generally close to the cardinal IPA values. Hawai‘i Creole has a seven vowel inventory, with additional low vowels in front and back position. With the exception of Kriol, vowel length is not phonemically distinctive.

Where vowel neutralization has occurred, these languages can show a fairly regular correspondence between the creole words and their corresponding English etyma. For example, in Bislama the English vowels START, TRAP and STRUT regularly correlate with /a/. However, the correspondences are not always predictable; the NURSE vowel in Bislama, for example, can correspond to /o/, /a/ and /e/.

Diphthongs are usually monophthongized (FACE is typically realized as [e]; GOAT as [o]). There is, however, considerable variation, especially word-finally. For example, centering diphthongs with a schwa off-glide (corresponding to postvocalic /r/ in rhotic varieties) in words such as more and where vary between monophthongal variants /o/ and /e/ and vowel sequences of /oa/ and /ea/. Generally speaking, better-educated speakers are more likely to contrast diphthongized and monophthongal vowels and have at their disposal a greater range of diphthongs.

Some of these varieties have rules of vowel harmony, especially between affixes and stems. For example, the Melanesian Pidgin varieties and the Australian creoles have in common a transitive verb suffix -Vm where the vowel harmonizes with the final vowel of the verb root. In Solomon Islands Pijin, vowels that are inserted within consonant clusters and word finally also typically harmonize; for example sukulu ‘school’, tarae ‘try’, bisinisi ‘business’.