The U.S. Geological Survey (USGS) assessed undiscovered, technically recoverable conventional oil and gas in 10 basins of India and Sri Lanka, as part of its assessment of the world's conventional resources: the Upper Assam, Mahanadi, Krishna-Godavari, Cauvery, Mannar, Kerala-Konkan, Mumbai Offshore, Cambay-Barmer, Kutch and Laxmi basins.
The 10 conventional assessment units in India and Sri Lanka. USGS.
How the basins formed
The basins record the tectonic history of India:
| Time | Event |
|---|---|
| Permian–Triassic | Gondwana began to break up along old lines of weakness, forming the Karoo rifts, with coal and lake mudstones as possible source rocks |
| Late Triassic–Early Jurassic | rifting continued, lifted by the heat of the Réunion mantle plume |
| Late Jurassic | Greater India — India, Madagascar, the Seychelles and Sri Lanka — rifted from Africa, forming the western-margin Kerala-Konkan, Mumbai Offshore, Cambay-Barmer and Kutch basins |
| Early Cretaceous | Antarctica split from eastern India, forming the Mahanadi, Krishna-Godavari, Cauvery and Mannar basins |
| Late Cretaceous | Madagascar rifted away; at the end of the Cretaceous the Seychelles block separated, forming the Laxmi Basin |
| Cretaceous–Paleocene boundary | the plume poured out up to 2,000 m of lava — the Deccan traps — over southwestern India; uplift tilted India east, turning its rivers to flow east and building big sediment wedges on the eastern margin |
| Late Eocene–Oligocene | India began colliding with Eurasia, and up to 20 km of sediment piled up in the Indus and Ganges deltas |
| Oligocene–Pliocene | the West Burma terrane's collision made the Naga Thrust Belt and the Upper Assam foreland |
Source rocks
The assessment defined one Mesozoic–Cenozoic Composite Total Petroleum System, with source rocks from Permian to Miocene. Geochemical data are meager: offshore wells have sampled mostly shallow, gas-prone delta sediments, while deep rift and distant marine mudstones — possibly major sources — are barely sampled. In rough order of importance, the likely sources are:
- Paleogene marine mudstones — generally the main source;
- Lower Cretaceous rift and post-rift mudstones;
- Upper Cretaceous marine mudstones;
- Permian coals (a gas source in Krishna-Godavari);
- Upper Jurassic–Lower Cretaceous rift lake mudstones (possible in Kutch and Cambay-Barmer).
Gas hydrates in the Krishna-Godavari and Mahanadi basins hint at a Miocene–Pliocene source of biogenic gas as well. More geochemical data would greatly help.
The estimates
Fully risked mean undiscovered resources for all 10 basins:
| Resource | Mean | Range (F95–F5) |
|---|---|---|
| Oil | 1,010 million barrels (1.0 billion) | 280–2,507 million barrels |
| Gas | 53,402 billion cubic feet (53.4 trillion) | 19,122–107,365 billion cubic feet |
| Natural gas liquids | 2,135 million barrels (2.1 billion) | 760–4,304 million barrels |
By basin, mean oil in oil accumulations and mean gas in gas accumulations:
| Basin | Oil (million barrels) | Gas (billion cubic feet) |
|---|---|---|
| Kerala-Konkan | 544 | 7,410 |
| Cambay-Barmer | 84 | 740 |
| Mannar | 87 | 11,338 |
| Cauvery | 72 | 8,233 |
| Krishna-Godavari | 69 | 10,678 |
| Mahanadi | 56 | 7,824 |
| Mumbai Offshore | 42 | 1,847 |
| Upper Assam | 26 | 2,818 |
| Laxmi | 24 | — |
| Kutch | 6 | 641 |
F95 means a 95% chance of at least that much. The Laxmi basin has no gas-accumulation estimate and an assessment-unit probability of 0.4; the others 1.0. The input data are in a USGS data release (Schenk, 2025), and more results are on the USGS Energy Resources Program site.
Sources
Based on "Assessment of undiscovered conventional oil and gas resources of India and Sri Lanka, 2024," U.S. Geological Survey Fact Sheet, U.S. Geological Survey, by the USGS India and Sri Lanka Assessment Team (Christopher J. Schenk and others); a work of the United States government in the public domain.
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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