A Cretaceous marine invasion occupied a basin of regional extent through Venezuela and Colombia. The basin was severely limited and separated into smaller basins of marine and nonmarine affinities during the Tertiary. Three principal sedimentary cycles since early Cretaceous time embrace the oil-bearing sedimentary section. Behavior of cratonic elements, formation of mobile belts, associated shifting of depositional conditions, and the evolving structural and stratigraphic pattern are described. Contour, isopach, and paleogeographic maps are presented, and restored volumes of sediments cited. Beneath the Maracaibo Basin is a crystalline mass which influenced development of a platform and shelf area respectively during Cretaceous and part of the Tertiary. A summary of oil istribution and geologic aspects of Maracaibo Basin oil fields is also included. History of oil field development is summarized.

Sedimentary facies, hinge belts, and evolving structural conditions have probably influenced oil accumulation. Opinions on probable source beds for oil in the basin are expressed. Nearly three fourths of the estimated ultimate known reserve is found in clastic, shallow-marine to brackish-water Oligo-Miocene and Eocene rocks associated with an unconformity and an Eocene hinge belt. Nearly one sixth is found in fractured Cretaceous limestones associated with anticlinal structures and a Cretaceous hinge belt. The remaining reserves are found in a shelf area shoreward from the Eocene hinge belt.