The U.S. Geological Survey has released a fresh look at the Phosphoria Total Petroleum System, an oil and gas province that stretches across northwest Colorado and southwest Wyoming and has been part of the American energy story for more than a century. First tapped in the early 1920s, the system has already given up about 500 million barrels of oil and 2.5 trillion cubic feet of natural gas. The new assessment confirms that hydrocarbons remain, though in limited volumes, and paints a clear picture of a province that has entered late maturity.
According to the USGS, the Phosphoria still contains roughly 3 million barrels of recoverable oil and an estimated 666 billion cubic feet of natural gas at depths that can reach 15,000 feet. The numbers are modest compared to its historical output, but they offer important context for understanding the lifecycle of a petroleum system that has been producing for more than 100 years. Sarah Ryker, the acting director of the USGS, noted that assessments typically focus on resources that are undiscovered yet scientifically supported by geology. In this case, after decades of continuous development, the system is showing little oil potential but still holds a measurable amount of gas.
The geology of the Phosphoria system explains both its productivity and its limits. The primary source rocks are the Meade Peak Member and the Retort Phosphatic Shale Member of the Permian Phosphoria Formation. These units are unusually rich in organic matter, sometimes reaching 10 percent total organic carbon, far higher than the average mudstone or shale. Hydrocarbons generated in these layers migrated into conventional reservoirs below Cretaceous formations where they were trapped by structural and stratigraphic features. Much of the easy oil was tapped long ago, and what remains is largely gas, often at depths where recovery becomes challenging and in some cases sour, containing hydrogen sulfide that requires expensive treatment.
Geologists believe the system is still feeding hydrocarbons upward into shallower Cretaceous formations, which helps explain why these overlying reservoirs remain active and more economically attractive. The Phosphoria’s deeper reservoirs may not be the focus of new development, but its role as a source rock continues to matter to industry across the Rockies. For operators, the message is not to chase deep, marginal oil, but to consider how migration from the Phosphoria may support production in younger and shallower reservoirs.
The latest USGS release is part of a broader series of assessments in the Southwestern Wyoming Province. Earlier this year, the agency evaluated the Mowry Composite Total Petroleum System and identified far greater volumes of undiscovered hydrocarbons. Taken together, these studies give industry professionals and policymakers a clearer view of the province as a whole, helping them allocate capital and craft land management strategies that reflect both frontier opportunities and mature systems like the Phosphoria.
Economics remain a decisive factor. Accessing gas at depths of up to 15,000 feet is costly, and dealing with sour gas adds further expense. This makes the residual volumes less attractive to most operators unless gas prices rise or new technologies reduce treatment costs. Yet even in its twilight, the Phosphoria is not without significance. The data provided by the USGS informs federal and state agencies as they set policy for leasing and development, and it helps companies understand what remains in a system that has been producing since the era of wooden derricks and early cable tool rigs.
The Phosphoria Formation also carries importance beyond hydrocarbons. Its phosphorite beds have long been mined in Idaho for fertilizer production, and scattered occurrences of vanadium and uranium add to its resource potential. Current efforts under the Earth MRI program are investigating the formation’s critical mineral potential more closely, reflecting a national push to secure supplies of materials needed for modern energy technologies. This dual identity, as both a hydrocarbon source and a potential contributor to critical mineral supply chains, ensures that the Phosphoria will remain under scientific and industrial scrutiny even as its oil production winds down.
For oil and gas professionals, the story of the Phosphoria is not about new booms but about lessons learned from a mature system. It shows how prolific petroleum provinces evolve, how resource potential shifts from oil to gas, and how geological processes continue to drive migration into younger formations. It also highlights the importance of integrated resource thinking, where a single formation can provide not just oil and gas but also fertilizers and strategic minerals.
The USGS findings confirm what many in the industry have already observed in practice. The oil is nearly gone, the gas is still there but comes with challenges, and the true opportunity may be in monitoring how hydrocarbons continue to charge other reservoirs above the Permian source rocks. For policymakers, it is a reminder that assessments are not simply academic exercises but tools that shape leasing strategies and regulatory decisions. For industry, it is a signal to look elsewhere for major new reserves while respecting the ongoing role of the Phosphoria in the energy and resource landscape of the Rocky Mountain region.
After a century of output, the Phosphoria is no longer a growth story, but it remains an important one. It has delivered vast quantities of hydrocarbons, it continues to underpin production in overlying formations, and it is increasingly recognized for its mineral potential. Its story is one of transition rather than conclusion, and its role as both a producer and a teacher of geologic lessons will endure.
