The Isoko language is spoken in the Southern Part of Nigeria precisely in Delta State Nigeria, by the Isoko people. It is regarded as a dialect of the neighbouring Urhobo language.
Michael A. Marioghae, working with Peter Ladefoged in 1962, made one of a few audio recordings of sample Isoko words that are made available at the UCLA phonetics archive.
The Isoko vowel system is hardly reduced from that reconstructed for proto-Edoid. There are nine vowels in two harmonic sets, /i e a o u/ and /ɪ ɛ a ɔ ʊ/.