It rises on the border between the two countries, near the juncture of N'Gounié and Ogooué-Lolo provinces of Gabon, runs south along the border and then southwest through the Niari province of Congo, then enters the Nyanga province of Gabon and makes a sharp bend to the northwest. It passes through Nyanga's capital Tchibanga (the largest city on the river), then gradually bends around to the southwest again, running through a series of rapids before coming out onto a coastal plain and emptying into the Atlantic Ocean.
Lerique Jacques. 1983. Hydrographie-Hydrologie. in Geographie et Cartographie du Gabon, Atlas Illustré led by The Ministère de l'Education Nationale de la Republique Gabonaise. Pg 14-15. Paris, France: Edicef.