Depositional characteristics of the Miocene oil-bearing sandstones of southern Trinidad suggest deltaic origin. Trinidad is embraced by the modern Orinoco delta. At first sight, the conclusion appears logical, therefore, that the Cruse-Forest oil sandstones represent the proto-Orinoco delta, extending farther east in the Miocene than now. Closer study, however, reveals flaws in this interpretation. In adjacent eastern Venezuela a marine embayment occupied the region through which the supposed proto-Orinoco River would have flowed, and there is no suggestion whatever of a delta prograding eastward during the Miocene. The sandstone patterns in Trinidad and eastern-most Venezuela (Pedernales) point strongly to a southeasterly source of the Cruse-Forest sediments, whereas the Orinoco’s basin lies on the southwest. The suggestion arises that the proto-Essequibo River, rather than the proto-Orinoco, was the main source of the Cruse-Forest sedirrients.