The Isoko language is spoken in the Southern Part of Nigeria precisely in Delta State Nigeria, by the Isoko people. It is similar to the neighboring 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/.