Undiscovered Oil and Gas in Yemen: USGS Assessment, 2024

As part of an ongoing assessment of conventional oil and gas in priority regions of the world, the U.S. Geological Survey (USGS) estimated the undiscovered, technically recoverable conventional oil and gas resources of three Mesozoic basins in Yemen: the Sab'atayn, Say'un-Masila and Jiza-Qamar basins.

The three conventional assessment units in Yemen. U.S. Geological Survey.

How the basins formed

The basins follow structures laid down in the Neoproterozoic. The northwest–southeast Najd fault system of that era was reactivated as a transtension system in the Mesozoic, when the Cimmerian terranes and Greater India broke away from the northeastern margin of Gondwana and opened the Neo-Tethys Ocean. In the Late Jurassic and Early Cretaceous this formed northwest–southeast basins in southern Yemen and northeastern Somalia, which were then side by side as part of northeastern Africa. Left-lateral transtension in the Late Jurassic (Kimmeridgian) opened the Sab'atayn Basin first in the west, then the Say'un-Masila Basin, and finally the Jiza-Qamar Basin in the east, along with matching rift basins in Somalia.

When the sea intermittently reached the Sab'atayn Basin in the Tithonian, up to 1,500 meters of evaporites of the Sab'atayn Formation were laid down there, forming important traps and seals for oil and gas; the other two basins received none. All three are structurally complex, with faulted subbasins where oxygen-poor conditions allowed rich petroleum source rocks to accumulate. Later, seafloor spreading in the Gulf of Aden in the Oligocene and the opening of the Red Sea in the Miocene split Arabia from Africa, separating the once-continuous Yemen and Somalia rifts by about 300 kilometers. Those events reactivated faults in the Yemeni basins and may have let some oil and gas escape.

The petroleum system

The USGS defined a Mesozoic–Cenozoic Composite Total Petroleum System spanning the three basins.

• Source rocks: the main ones are organic-rich shales of the Upper Jurassic Madbi Formation, present in the Sab'atayn and Say'un-Masila basins and possibly the Jiza-Qamar, with up to 20 weight percent total organic carbon and up to 600 meters thick. Others are the Lower Cretaceous Saar Formation, a major source in the Jiza-Qamar Basin; the Upper Cretaceous Harshiyat Formation, possibly in all three basins; and the Upper Cretaceous Mukalla Formation in the Jiza-Qamar Basin, whose coal beds may be an important source of gas.
• Reservoirs: river-delta, nearshore marine and turbidite sandstones, platform carbonates and fractured basement rock, including the Lower Cretaceous Qishn sandstones.
• Traps and seals: traps are mostly structural, with some stratigraphic traps in deepwater sandstones and platform-margin carbonates. Tithonian salt forms the seals in the Sab'atayn Basin; in the other two, low-permeability Qishn Formation carbonates seal the Qishn sandstones beneath them.

The assessment divided the system into three conventional assessment units, one for each basin's reservoirs.

Results

The estimated mean undiscovered resources for Yemen are:

• Oil: 261 million barrels (about 0.26 billion), with a range from 95 million (95% chance of at least this much) to 558 million barrels (5% chance);
• Gas: 4,514 billion cubic feet (about 4.5 trillion), ranging from 1,034 to 11,878 billion cubic feet;
• Natural gas liquids: 122 million barrels, ranging from 29 to 323 million barrels.

By basin, the mean estimates are:

Smaller amounts of gas are also estimated in the oil fields (126, 152 and 112 billion cubic feet, respectively), along with natural gas liquids in both kinds of field. All estimates are fully risked, and each unit was given a probability of 1.0 of containing at least one field of minimum size.

Sources

• U.S. Geological Survey, Yemen Assessment Team (Christopher J. Schenk and others), "Assessment of undiscovered conventional oil and gas resources of Yemen, 2024," Fact Sheet 2025–3047. https://pubs.usgs.gov/publication/fs20253047/full
• Input data are summarized in the fact sheet and in Schenk (2025). The fact sheet draws on Redfern and Jones (1995), Ellis and others (1996), Ahlbrandt (2002), As-Saruri and Sorkhabi (2014), Hakimi and others (2012–2020) and Nonn and others (2019), among others.
• USGS Energy Resources Program: https://www.usgs.gov/programs/energy-resources-program