Ethnologue: Languages of the World, 18th Edition . (2015) · edited by Lewis, M. Paul, Gary F. Simons, and Charles D. Fennig · SIL International http://www.ethnologue.com

Sepik languages: checklist and preliminary classification . Laycock, Donald C. (1973) · Pacific Linguistics · edited by Wurm, Stephen A. · Australian National University, Research School of Pacific Studies, Department of Linguistics

Referent Management in Olo: A Cognitive Perspective . Staley, William E. (2007) · SIL e-Books · SIL International