High Quality Content by WIKIPEDIA articles! The Sobat River is a river in South Sudan, Africa. The most southerly of the great eastern tributaries of the Nile, the Sobat enters the White Nile at Doleib Hill, near the city of Malakal in the Upper Nile state of South Sudan. The Sobat River is formed by the confluence of the west-flowing Baro River and the north-flowing Pibor River, on the border with Ethiopia.