The determination and division of petroleum systems might be a key problem for the hydrocarbon exploration, namely, how to choose a prospective target area. The correlation of oil-source rocks must be the key to determine petroleum systems. In case that no mature source rock samples were available, to integrate the geological characteristics with the evolution history of oil pools should be a scientific way to divide petroleum systems. Based on the geological and geochemical analyses, this paper took two oilfields in the same structural rise of Nugara Subbasin, Muglad Basin in Sudan, Central Africa, as an example, and divided the subbasin into two independent petroleum systems. The authors found that the oils of two oilfields might be sourced from different systems. This idea should be interested to forecast petroleum prospects in rift basins with complicated tectonic evolution.