The phonological inventory of consonants is atypically large for an Oceanic language. Many sounds which are allophones in other sub-families are distinct phonemes in the Nengone language:[2]
Tryon, D.T. and Dubois, M.J. Nengone dictionary. Part I: Nengone-English. C-9, viii + 452 pages. Pacific Linguistics, The Australian National University, 1969. doi:10.15144/PL-C9
Tryon, D.T. and Dubois, M.J. Nengone dictionary. Part II: English-Nengone. C-23, iv + 205 pages. Pacific Linguistics, The Australian National University, 1971. doi:10.15144/PL-C23