Along the coast of Peru, the shelf between the Andes Mountains and the 100-fm isobath is narrow, about 100 km wide in a few places. Between lat. 6 and 14°S nearly all of it is a wide offshore shelf. This shelf has been the site of marine deposition throughout the Tertiary. Basement highs and irregularities define six subbasins. In the north, the mainly offshore Progreso basin extends into Peru from the Gulf of Guayaquil. It is filled with upper Tertiary shales, sands, and conglomerates with a maximum thickness of 6,000 m. The small abandoned Zorritos field was in this basin and some undeveloped 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, is both onshore and offshore. Sedimentary rocks consist of Upper Cretaceous and lower Tertiary silicate clastic rocks with a maximum thickness of 8,000 m, but 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 large undiscovered potential, but the offshore is estimated to have a potential of one billion bbl. The Sechura basin is between the Andes and a discontinuous chain of low coastal mountains which separates it from the Talara basin. It is mostly onshore but extends southward onto the offshore. Up to 3,000 m of marine, brackish, and nonmarine sedimentary rocks, i cluding diatomite and phosphatic and tuffaceous elements, fill the basin. Most of the strata are upper Tertiary, but lower Tertiary and Cretaceous beds also are present. In the 1950s, 28 wildcat wells were drilled with the discovery of moderate reserves of gas. A total potential for the basin is estimated to be 100 million bbl.

The Salaverry basin is the largest of the coastal basins. It is 500 km long and up to 100 km wide, is entirely offshore, and extends to within 100 km of Lima. It contains up to 3,000 m of Tertiary marine shales, silts, and calcareous sedimentary rocks with sandstones at the base. Two wells have been drilled in this basin and the estimated potential for the basin is 500 million bbl. The Pisco basin begins about 100 km south of Lima in the offshore, but southward splits into onshore and offshore parts. Up to 2,000 m of lower and upper Tertiary sedimentary rocks are present. The lower Tertiary is composed of conglomerates, sandstones, and calcareous shales. The upper Tertiary consists of sediments similar to those of the upper Tertiary in the Sechura basin. One well has been drilled in t e 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 sediments 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 two billion bbl.

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