Along the coast of Peru, the shelf between the Andes mountains and the 100-fm isobath is narrow and reaches a width of 100 km in few places. Between lats. 6 and 14°S, nearly all the shelf lies offshore. This shelf was the site of marine deposition throughout the Tertiary. Basement highs and irregularities define six subbasins. Beginning in the north, the mainly offshore Progreso basin extends into Peru from the Gulf of Guayaquil. It is filled with upper Tertiary shales, sandstones, and conglomerates with a maximum thickness of 6,000 m. The small, abandoned Zorritos field is located in this basin, and some oil and gas have been discovered recently. The basin has an estimated potential of 350 million bbl.

The Talara basin, which has produced over 800 million bbl of oil, is both onshore and offshore. The strata are Upper Cretaceous and lower Tertiary silicate clastic rocks with a maximum thickness of 8,000 m; nearly all production comes from Eocene deltaic, fluvial, and turbidite sandstones. Intense block faulting, gravity sliding, and submarine slumping complicate development operations. The onshore part does not have significant potential for future discoveries, but the offshore is estimated to have a potential of 1 billion bbl. The Sechura basin is situated between the Andes and a discontinuous coastal chain of low mountains which separates it from the Talara basin. It is mostly onshore but extends offshore to the south. Up to 3,000 m of marine, brackish, and nonmarine deposits, incl ding diatomite and phosphatic and tuffaceous elements, fills the basin. The most widespread sedimentary rocks are upper Tertiary, but lower Tertiary and Cretaceous rocks are also present. In the 1950s, 28 wildcat wells were drilled and moderate reserves of gas were discovered. Total potential for the basin is estimated to be 100 million bbl.

The Salaverry basin, the largest of the coastal basins, has a length of 500 km and a width up to 100 km. Entirely offshore, it extends southward to about 100 km north of Lima. It contains up to 3,000 m of Tertiary marine shales, siltstones, and calcareous rocks with sandstones at the base. Two wells have been drilled in this basin. The estimated potential for the basin is 500 million bbl. The Pisco basin begins about 100 km south of Lima in the offshore, but splits into onshore and offshore parts southward. Up to 2,000 m of lower and upper Tertiary rocks are present. The lower Tertiary is composed of conglomerates, sandstones, and calcareous shale. The upper Tertiary consists of strata similar to those of the upper Tertiary in the Sechura basin. One well has been drilled in the basin. The estimated potential for the basin is 100 million bbl. The Moquegua basin is a narrow onshore basin between the Andes and the coastal chain of mountains. Marine strata are found only in the northern part and are of insufficient volume to have significant potential. The total potential of the coastal basins is estimated to be about 2 billion bbl.