The U.S. Geological Survey (USGS) has assessed the undiscovered, technically recoverable conventional oil and gas in the Permian Phosphoria Total Petroleum System (TPS) of the Southwestern Wyoming Province — parts of Wyoming, Utah and Colorado. The last such assessment was in 2005. It rests on the system's geology — source rocks, reservoirs, traps, seals and timing — and on the history of exploration and discovery.
The answer
| Resource | Mean estimate | Range (F95–F5) |
|---|---|---|
| Gas | 666 billion cubic feet | 187–1,480 billion cubic feet |
| Natural gas liquids | 20 million barrels | 6–44 million barrels |
| Oil | 3 million barrels | 1–5 million barrels |
F95 means a 95% chance of at least that amount; F5, a 5% chance. Estimates are fully risked. Almost all the gas — a mean of 661 billion cubic feet — is expected in gas accumulations.
The Sub-Cretaceous Conventional Oil and Gas Assessment Unit. USGS
Where the oil and gas come from
The main source rocks are two members of the Permian Phosphoria Formation:
| Member | Thickness |
|---|---|
| Meade Peak Member | up to 50 meters |
| Retort Phosphatic Shale Member | up to 33 meters |
Both occur in west-central Wyoming and eastern Idaho and don't extend east across the system. These organic-rich mudstones hold up to 10% organic carbon by weight, with oil-prone Type IIS kerogen. In the west-central part of the system, models show them reaching the temperature for oil generation about 85 million years ago.
How far — and when — that oil migrated east is debated. Within the system, 18 stratigraphic units older than the Cretaceous have produced Phosphoria-sourced oil and gas, usually from structural traps, sometimes stratigraphic or combination traps.
The assessment unit
The USGS defined one unit, the Sub-Cretaceous Conventional Oil and Gas Assessment Unit, covering the whole province. The model: oil and gas from Phosphoria mudstones migrated east into pre-Laramide stratigraphic and structural traps, and some later moved again into Laramide-age traps.
- Reservoirs: mainly the Flathead Sandstone, Madison Limestone, Tensleep Sandstone, Weber Sandstone, Phosphoria Formation, Nugget Sandstone and Morrison Formation — though most production has come from the Pennsylvanian Tensleep and Weber Sandstones.
- Gas from oil: Phosphoria oil in the deep centers of the Greater Green River, Great Divide, Washakie and Sand Wash basins may have turned to gas — thought to be the main potential resource.
- Drilling so far: more than 1,000 wells have produced from these older rocks, mostly along the edges of the system, where oil dominates.
| Key inputs | Min | Median | Max | Mean |
|---|---|---|---|---|
| Oil fields | 1 | 3 | 6 | 3.1 |
| Gas fields | 1 | 20 | 80 | 22.1 |
| Oil field size (million barrels) | 0.5 | 0.7 | 10 | 0.9 |
| Gas field size (billion cubic feet) | 3 | 12 | 1,000 | 30.1 |
Results are also at the USGS Energy Resources Program.
Sources
Based on Drake RM II, Hearon JS, Mercier TJ, Le PA, Leathers-Miller HM, Gelman SE, Johnson BG, Lagesse JH, Cicero AD, Schenk CJ, Tennyson ME, "Assessment of undiscovered conventional oil and gas resources in the Phosphoria Total Petroleum System of the Southwestern Wyoming Province, 2024," U.S. Geological Survey Fact Sheet 2025–3031, USGS; a work of the United States government in the public domain. Input data: Drake (2025), doi:10.5066/P1EE7PQT.
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