The Paleozoic petroleum system of the Central and Northern Provinces of Saudi Arabia contains one of the most prolific oil-prone source rocks of Silurian age worldwide, the Qusaiba shale of the Qalibah Formation. This source rock is responsible for charging the large, gentle structures of the Central Province with billions of barrels of light, sweet, crude oil. Organic geochemical methods such as biomarkers, organic petrography, and characterization of the source rock facies have been used to determine the most likely candidate source rock for the Paleozoic oils of Saudi Arabia. By using detailed extract and oil characterizations, the basal «hot» shales of the Qusaiba Member of the Silurian Qalibah Formation have been correlated to the oils reservoired in the Permian sands of the Central Province of Saudi Arabia.