The Mowry Shale is the main source rock for most of the Upper Cretaceous reservoirs in Wyoming's Powder River Basin, including the Niobrara, Turner, Parkman, Shannon and Sussex that operators drill today. Estimates going back to Momper and Williams (1984) put the oil it generated at close to 12 billion barrels. Since the late 2000s it has also been drilled directly as a horizontal target, and the Wyoming State Geological Survey lists it among the basin's five most productive reservoirs in 2024 alongside the Frontier, Niobrara, Parkman and Turner.

It remains an early-stage play. Thick, laterally continuous bentonite (altered volcanic ash) beds absorb fracture energy and have complicated completions, results have been inconsistent from one pad to the next, and the horizontal well count is small next to the Niobrara and Turner. Analysts at Novi Labs still describe the Mowry as "very underexplored." Two publicly funded research programs, a $14.9 million U.S. Department of Energy field laboratory and a University of Wyoming study backed by $2.5 million from the Wyoming Legislature, are aimed squarely at those completion problems.

Where it fits for investors: the Mowry is the kitchen that charged the shallower rock. Kingdom Exploration's current Powder River program drills the Niobrara and Shannon, not the Mowry itself, but the Mowry's richness is the reason those reservoirs are oil-charged in the first place.

Mowry development has come in steps:

• Pre-2008: Recognized mainly as a source rock. Roughly 1.2 billion barrels of oil and 2.2 trillion cubic feet of gas had been produced from Mowry-sourced reservoirs across the basin (USGS, 2008).
• 2008: The USGS assessed the Mowry as a continuous (shale) hydrocarbon system in the Powder River Basin for the first time, estimating a mean 198 million barrels of undiscovered, technically recoverable oil plus 198 billion cubic feet of gas.
• 2008 to 2018: Early one-mile horizontal wells rarely reached commercial rates. Operators concentrated on the shallower, oilier Niobrara, Turner and Parkman instead.
• 2019: Powder River tight-oil output passed 80,000 barrels a day, led by the Turner (about 67,000 b/d). The Mowry contributed roughly 3,000 b/d (DOE/NETL).
• 2021 to 2022: A DOE/NETL field laboratory in the southern basin, operated with Occidental, drilled a vertical pilot hole that recovered 191 feet of Mowry core, plus Niobrara and Turner horizontals for monitoring.
• 2022 to 2023: The Wyoming Legislature funded a University of Wyoming School of Energy Resources Mowry program ($2.5 million, with a further $500,000 to the Wyoming Energy Authority for preliminary work). Phase II selected 13 faculty projects in September 2023.
• 2024 to 2025: Anschutz Exploration, the basin's largest private operator, moved from a pilot into an early Mowry program; a 10,000-foot-lateral Mowry well that came online in July 2024 averaged about 1,000 barrels of oil a day through April 2025. Continental Resources filed applications for additional horizontal Mowry wells in Campbell and Converse County units, and acquisition filings in August 2025 listed about 270 Mowry locations in one private operator's inventory.

Key characteristics of the Mowry Shale:

• Age and setting: Lower Cretaceous (Albian, roughly 98 million years old), deposited in the low-energy, oxygen-poor Mowry Sea on the western side of the Western Interior Seaway.
• Lithology: Siliceous, fish-scale-bearing shale with numerous bentonite beds. Two of them, the Clay Spur and Arrow Creek bentonites, are continuous enough to serve as time markers across Wyoming and Montana.
• Thickness: Generally 150 to 250 feet, thickening from southeast to northwest across the basin.
• Depth: Roughly 7,000 to 8,000 feet in the Dry Fork area northeast of Gillette, deepening to 10,000 to more than 12,000 feet toward the basin axis in Converse and Johnson counties.
• Organic richness: Average total organic carbon of about 5 to 7 weight percent, increasing from southwest to northeast (University of Wyoming, 2024).

The bentonites are the central engineering problem: they are soft, laterally continuous and act as fracture barriers, so a frac design that works in the Niobrara does not transfer directly to the Mowry.

Reservoir properties reported in public research:

Powder River Basin context:

• The basin has produced more than half of Wyoming's oil every year since 2014 and more than 70% from 2022 through 2024 (Wyoming State Geological Survey).
• The Mowry Shale was among the basin's five most productive reservoirs in 2024, with the Frontier, Niobrara, Parkman and Turner.
• Mowry horizontal wells remain a small share of basin activity, concentrated in Campbell, Converse and Johnson counties. Results have been inconsistent: strong delineation wells have been followed by weaker pad-development results (Enverus, January 2025).
• The best publicly reported recent well, an Anschutz Mowry horizontal with a 10,000-foot lateral, produced more than 279,000 barrels of oil from late July 2024 through April 2025, about 1,000 barrels a day, after a 24-hour initial rate of 2,056 barrels of oil and about 1.5 million cubic feet of gas.
• University of Wyoming researchers describe the typical Mowry decline curve as a quick peak followed by a long, relatively stable tail, which they attribute to a strong gas drive. Volumes vary widely by location.

Drilling and completion practice is still evolving:

• Lateral length: Two-mile (about 10,000-foot) laterals are the basin standard. Three-mile laterals arrived in 2024 and 2025: Devon had drilled 38 and Continental 33 across the basin by November 2025, and Anschutz drilled its first three-mile Mowry and Niobrara wells on a Johnson County pad in mid-2025. Enverus reports no production degradation from the third mile.
• Completion intensity: Powder River completions average more than 2,000 pounds of proppant per lateral foot, about double the Williston Basin (Enverus).
• Bentonite challenge: Frac designs must be modified so energy is not lost into the soft bentonite beds. Lab work at the DOE/NETL field laboratory tested un-propped crack behaviour and proppant embedment in Mowry versus Niobrara samples to guide those designs.
• Well cost: Operators do not publish per-well Mowry costs. Wyoming two-mile horizontal wells were quoted at roughly $12 to $13 million in late 2025 (Kirkwood Oil & Gas), and a well pad alone can exceed $1 million. Water is comparatively expensive because surface water covers less than 1% of the basin and landowners control it.

Mowry economics are improving but still trail the core Powder River zones:

• Breakeven: Enverus put the average breakeven for the basin's Mowry and Niobrara wells at about $60 to $65 a barrel, falling to roughly $55 with three-mile laterals; a few operators are already below $50 (November 2025). Anschutz says its own breakevens are "well below $60."
• Consistency risk: The main economic issue is variability. A single strong well does not yet prove a repeatable pad program in the Mowry.
• Cost structure: Development is more expensive than in the Permian, Bakken or DJ Basin, so Powder River producers cut activity faster when prices fall.
• Upside: Publicly funded research is targeting the completion problem directly, and longer laterals have already pulled breakevens down.

The resource is large relative to what has been produced:

• Mean undiscovered, technically recoverable resource of 198 million barrels of oil, 198 billion cubic feet of gas and 11.9 million barrels of natural gas liquids (USGS, 2008). The USGS has said an updated Powder River assessment could come as soon as 2026.
• Close to 12 billion barrels of oil originally generated by the formation.
• Operators are delineating the Mowry while developing the Niobrara, Turner and Parkman above it, so the Mowry is being de-risked largely with infrastructure that is already paid for.
• Note: the USGS's 2025 estimate of 473 million barrels for the "Mowry Composite" system covers southwestern Wyoming, Colorado and Utah, not the Powder River Basin.

The Mowry Shale is the engine of the Powder River Basin and, for now, a harder target than the reservoirs it charged. Direct Mowry drilling is real but early: a handful of operators, inconsistent pad results, and a completion problem that two research programs are still working on. The practical takeaway for an investor is that the Mowry's richness is what makes the Niobrara, Shannon and Turner above it attractive today, while the Mowry itself is a longer-dated opportunity that will reward operators who solve the bentonite problem first.