Endangered Languages Catalogue Project. Compiled by research teams at University of Hawai'i Mānoa and Institute for Language Information and Technology (LINGUIST List) at Eastern Michigan University . (2012) ·

Endangered Languages in West Africa ( pp. 140-162 ch. 7 ) . Roger Blench (2007) · In Language Diversity Endangered Trends in Linguistics, Studies and Monographs · edited by Matthias Brenzinger · Mouton de Gruyter

"Documenting Defaka [afn] and Nkoroo [nkx]" NSF DEL Abstract . Akinbiyi Akinlabi (2007) · http://nsf.gov/awardsearch/showAward.do?AwardNumber=0553971&version=noscript

Africa ( ch. 7 ) . Gerrit J. Dimmendaal and F. K. Erhard Voeltz (2007) · In Encyclopedia of the World's Endangered Languages edited by Christopher Moseley · Routledge

The World Atlas of Language Structures . (2005) · edited by Bernard Comrie and David Gil and Martin Haspelmath and Matthew S. Dryer · Oxford University Press

An Atlas of Nigerian Languages . Roger Blench (2011) · Mallam Dendo http://www.rogerblench.info/Language/Africa/Nigeria/Atlas%%20of%%20Nigerian%%20Languages-%%20ed%%20III.pdf

Defaka & Nkoroo Description & Documentation . Akinbiyi Akinlabi and Bruce Connell and Ozo-Mekuri Ndimele (2011) · http://defaka.rutgers.edu/project.html

Atlas of the World’s Languages in Danger . Christopher Moseley (ed.) (2010) · UNESCO Publishing http://www.unesco.org/culture/en/endangeredlanguages/atlas

Defaka: Ijo's Closest Relative ( pp. 85-111 ) . C. E. W. Jenewari (1983) · In Current Approaches to African Linguistics edited by Ivan R. Dihoff · Dordrecht: Foris Publications

Defaka and ex͡tsubdotIjex͡tsubdoto: A reassessment of the Ijoid relationship . Bruce Connell and William Bennett and Inoma Essien and Ebitare Obikudo and Ozo-mekuri Ndimele and Akin Akinlabi (2009) ·

Defaka, Ijo's Closest Linguistic Relative ( pp. 85-111 ) . Jenewari, Charles E. W. (1983) · In Current Approaches to African Linguistics 1 Publications in African Languages and Linguistics · Vol. 1 · edited by Dirhoff, Ivan R. · Foris

Defaka: Ijo’s closest linguistic relative ( pp. 54 ) . Jenewari, Charles E.W. (1983) · Delta series, #2 · Univ. of Port Harcourt Press

Defaka: Ijo’s closest linguistic relative ( pp. 85-111 ) . Jenewari, Charles E.W. (1983) · In Current approaches to African linguistics 1: selection of papers read at the 11th annual conference on African linguistics, April 11-12, 1980, Boston University Publ. in African languages and linguistics (PALL), #1 · edited by Dihoff, Ivan R. · Mouton de Gruyter; Foris Publ.