Summary

Millions of people in the United States live within 1 mile of an orphan oil or gas well, defined as a documented hydrocarbon well without a responsible party or owner that has yet to be adequately plugged (Kang et al. 2023; Meehan et al. 2025; Peltz 2022).¹ Nationwide, orphan wells are estimated to number just under 118,000 (Merrill et al. 2023).² Millions more people in the United States live near undocumented wells. Undocumented wells are those drilled early in the history of oil and natural gas production, typically before the advent of government regulation in the 1890s, and their locations are unknown. Estimates of the number of undocumented wells vary widely, from 250,000 to 740,000 nationwide (IOGCC 2024). Pennsylvania and Oklahoma alone may contain over 600,000 undocumented wells (Jahan et al. 2025).³

Orphan wells, undocumented wells, and even some abandoned wells—those wells plugged and properly decommissioned according to the regulatory requirements in place at the time—may pose public health, safety, and environmental hazards. The lack of a plug or barrier or the failure of existing barriers may create a migratory pathway for hazardous fluids or gases, and a combination of chemical, geological, or mechanical stresses over time affects the potential for such pathways to occur (Yousuf et al. 2021). Leaking wells can expose nearby inhabitants to air and water pollution, degrade local ecosystems, and impact the use of the surface land and subsurface resources.

Hydrocarbon wells are found in 38 states; most are located on private land and thus fall under the regulatory authority of state governments (NASEM 2025). State

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¹ See Box 1-2 for further information on key terms and definitions used throughout this report.

² See Merrill et al. (2023) for data gaps contributing to this estimate.

³ These estimates are by their nature imprecise. For the Interstate Oil & Gas Compact Commission report (IOGCC 2024), some states reported a wide range in the estimated number, and others were unable to provide any reliable estimate. Jahan et al. (2025) used historical well and production data to arrive at their estimates. States are working to better define the numbers, location, and risks of undocumented wells.

governments were also the first to regulate the oil and gas industry, including the plugging of wells (see Figure 2-1 in Chapter 2). In 1935, state governments also formed what is today the Interstate Oil & Gas Compact Commission (IOGCC) to work together on common regulatory issues. Today, the IOGCC collectively represents the governors of oil- and gas-producing states and serves as an authority for oil and gas regulation. For wells on federal lands, the appropriate federal land management agency has a key role. Tribal oil and gas agencies and their federal partners at the Bureau of Indian Affairs have jurisdiction on Tribal lands.

States and operators have been plugging, and in some cases re-plugging, orphan wells for decades, with particularly concerted activity beginning in the 1990s (IOGCC 2000). Recent federal funding has accelerated state plugging efforts. In 2021, the Infrastructure Investment and Jobs Act (IIJA) established the Orphaned Wells Program Office (OWPO) within the Department of the Interior and provided approximately $4.7 billion in grants for federal, state, and Tribal agencies to plug and remediate orphan wells and well sites on their lands. As of June 2025, states, federal agencies, and Tribal governments have used program funds to plug and reclaim more than 10,500 orphan wells (OWPO 2025). Funds will remain available through 2030.

At the request of OWPO, the National Academies of Sciences, Engineering, and Medicine convened a committee of volunteer experts to provide advice on regulatory, technical, scientific, and economic considerations for plugging and remediating orphan and abandoned oil and gas wells. In addition to an assessment of current plugging practices and technologies, OWPO sought information on the causes, frequency, and prevention of plugged well failures. The committee was also asked to consider post-plugging monitoring and risk management, including public disclosure, as a means to achieve long-term health and safety benefits. Finally, OWPO tasked the committee with identifying future research and development areas for industry and federal agencies to pursue.

STATES ARE CENTRAL TO THE SOLUTION

Identifying and plugging an orphan well is a complex undertaking, especially since drilling and plugging technologies, regulations, and record-keeping standards have continued to evolve since the first commercial well was drilled in 1859. Records of information key to a successful plugging—such as a well’s type, depth, construction materials, and last production date—may not be available. In addition, drilling technologies have been adapted to their geological contexts; for example, the drilling technologies used in the Appalachian Basin in the late 1800s differ greatly from those used in the Permian Basin in the 1920s and later. These geological contexts also affect the types of risks that orphan wells present. Consequently, states have developed their own guidelines and standards for choosing plug materials and placement, witnessing a plugging procedure, post-plug monitoring, and ranking the priority of wells to plug.

The development of regulations at the state level continues to inform industry standards. State programs are responsible for the vast majority of orphan wells plugged historically and under IIJA grant funding. In addition, federal land management agencies often contract with states to plug orphan wells on federal lands (Croft 2024). IIJA funding has also increased the capacity of state and Tribal agencies to manage their

orphan wells, although capacity still varies among states and Tribes. Most onshore oil and natural gas development in the United States is regulated by state governments, which have developed the appropriate local expertise, knowledge, and data needed to lead most orphan well plugging efforts.

To learn more about the role of the states, the committee convened information-gathering sessions with industry experts and state representatives, co-located a committee meeting with the IOGCC Annual Business Meeting, and administered a questionnaire prior to meeting with IOGCC meeting attendees. From this information-gathering in conjunction with a review of literature and historical regulation, the committee concludes the following⁴:

Conclusion 2-1: States have had orphan well plugging programs for decades; these programs have developed core groups of professionals with the expertise and local knowledge to plug orphan wells in their jurisdictions.

VERIFYING BARRIERS

Verifying the locations and integrity of all well barriers is best practice in the plugging process (API 2021). Many, but not all, states require inspections or witnessing by a regulatory agency representative before, during, and after plugging.⁵

Conclusion 3-1: Verification of permanent barriers is a critical component of plugging operations to confirm barrier competence and full isolation, to help prevent environmental contamination, and to ensure public health and safety. Verification includes the critical steps of design review, inspection and testing, and documenting and witnessing.

Recommendation 3-1: Regulatory agencies involved in plugging and abandonment should require a barrier verification plan with defined acceptance criteria in the approved plugging plan. Agencies should specify when permanent barriers must be verified and the minimum methods to be used for inspection and testing (e.g., tagging, pressure testing, and logging). An agency representative should be on site to witness critical operations and confirm compliance, and verification results should be documented in post-plugging reports.

CONTINUED EFFORTS AND FUNDING SUPPORT

Industry and state regulatory agencies have developed best practices and standards for plugging hydrocarbon wells. Despite the associated uncertainties, state-level plugging programs have proven successful. Studies show that plugging orphan wells is an

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⁴ See Chapter 2 for supporting text.

⁵ Discussion among state representatives and plugging and abandonment contractors, public information-gathering session, July 22, 2025. See also Chapter 3 for supporting text.

effective approach to reducing leaks and emissions (Kang et al. 2016; Raimi et al. 2021; Wisen et al. 2020). Moreover, federal funding under the IIJA accelerated state activity, resulting in state orphan well programs plugging more than 10,000 additional wells as of June 2025 (OWPO 2025). Still, states’ long-running orphan well programs have plugged only a small fraction of the estimated numbers of orphan and undocumented wells.

Recommendation 3-2: Plugging orphan wells is effective for reducing leaks and emissions, and states should continue to focus on plugging orphan wells following best practices and accepted industry standards. Future federal and state funding should be considered to provide states added support for their work.

ROOT CAUSE ANALYSIS OF PLUGGED WELL FAILURES

The primary goals of wellbore plugging and abandonment are natural resource protection, interval isolation, and leak and cross-flow prevention. A plugged and abandoned well that fails to meet any one of these goals can be considered a failure. The committee was unable to complete a comprehensive well-failure root cause analysis because data on older wells are lacking and data on current plugged well failures are collected unsystematically. However, the committee outlined some factors and conditions that can lead to leaks and other negative impacts of plugged well failures and notes the development of predictive analysis tools that can be used if appropriate data are collected. Given the importance of improved data collection for future root cause analysis efforts, the committee identified the following conclusions and recommendation⁶:

Conclusion 3-2: Access to orphan well data is important to many stakeholders, including the public, the oil and gas industry, future users of the subsurface, and researchers. The most important data to collect are well drilling, construction, and operations records; approved well plugging procedures; and post-plugging reports.

Conclusion 3-3: Records of any observed variations from approved plugging procedures are valuable yet are not generally captured in existing forms. Collecting this information as a standard practice would enable pluggers to more accurately assess well integrity, help regulatory agencies continuously improve practices, and provide information needed if surrounding wells are repurposed.

Conclusion 3-4: There were not enough publicly available data (e.g., on well integrity, instances of failure, and actions to resolve failures) for the committee to complete a probabilistic assessment of well failures or to understand the likelihood of failures. Gathering information on well plug failures would be valuable to gain insight into their causes, frequency, and associated emission rates.

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⁶ See Chapter 3 for supporting text.

Recommendation 3-3: A reporting and corrective action system should be implemented to improve essential data collection and analysis of plugged well failures. Such a system could also provide common organization and storage for well drilling, construction, and operations records; approved well plugging procedures; and post-plugging reports.

MONITORING PLUGGED WELLS

Monitoring plugged wells is a solution to the risks associated with plugged well failures. Multiple techniques exist for monitoring the integrity of the well barrier or detecting the presence of leaks on the surface or in the subsurface. Since not all plugged wells present the same likelihood of failure or severity of consequences, monitoring can be prioritized according to a set of risk factors. Many states use a similar set of risk factors in their decision-making processes for prioritizing orphan wells for plugging. To incorporate risk factors into prioritizing wells for post-plug monitoring, the committee concludes and recommends the following⁷:

Conclusion 4-1: Pre-plugging prioritization rankings provide a baseline to determine potential risks associated with orphan wells. Post-plug monitoring prioritization and planning could use existing pre-plug prioritization frameworks as models.

Recommendation 4-1: States should work toward establishing risk factor-based monitoring prioritization frameworks to determine which wells and what type of post-plug monitoring should be prioritized.

REMEDIATION AND RECLAMATION

Remediating failed orphan wells includes reclaiming the associated surface area, typically either to original condition or otherwise restoring the character and productivity of the land and water. After reviewing subsurface conditions that can affect remediation and reclamation, and reclamation methods, the committee concludes the following⁸:

Conclusion 5-1: Orphan well sites may exhibit releases of oil, produced water, or other fluids to the surface. In the subsurface, geologic characteristics such as porosity, permeability, fluid content, and faulting can impact the ability of contaminants to migrate across multiple zones within a wellbore and affect groundwater aquifers. Priorities for site reclamation include containing and preventing leaks and ensuring reclamation is achieved according to state regulatory requirements.

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⁷ See Chapter 4 for supporting text.

⁸ See Chapter 5 for supporting text.

NEW TECHNOLOGIES AND WELL PLUGGING IN THE FUTURE

The committee considered the landscape of new technologies and potential advances across all stages of a well plugging operation, including for locating orphan wells, wellbore assessment, plug materials and practices, and verification and monitoring. It identified areas of promise such as artificial intelligence (AI) for wellbore assessment and cement alternatives for plug materials. New materials, technologies, and practices—despite their potential—present a challenge for state regulators and industry stakeholders, given that no standardization exists for assessing the validity of advances in these areas. Widespread adoption of new technologies is hampered by a complex network of financial, institutional, regulatory, and public perception barriers. A notable “regulatory lag” exists in that standards have not kept pace with technological advancements, creating a paradox: stakeholders may favor the known costs of traditional methods over the perceived risks of unapproved solutions.⁹

Conclusion 6-1: It is challenging to test new technologies under subsurface and laboratory conditions that match local geologic factors. This can impact both commercial and regulatory decision-making around their use. Other countries have successful collaborations focused on new technologies and testing; these can provide exemplars for the United States.

Recommendation 6-1: The Orphaned Wells Program Office, in collaboration with the Department of Energy and other relevant federal agencies, state and Tribal agencies, academia, and industry, should explore a mechanism to share information among themselves for the purpose of demonstrating the effectiveness of new and evolving technology to improve well plugging practices, materials, and monitoring. This may be a common system for collecting and sharing qualification test results or a more formal testing program.

WORKFORCE READINESS

The committee also identified a broader issue related to future technological advances: the workforce for well plugging continues to shrink and will need to be trained not only in the basics of well plugging best practices but also in newer techniques, such as applying AI methods.¹⁰

Conclusion 6-2: There is a workforce readiness gap in plugging and remediation. The need for workers skilled in oil, natural gas, and geothermal well servicing, including well plugging and abandonment, will continue to grow for the foreseeable future. Universities, technical schools, industry associations, and chambers of commerce all play roles in generating interest among prospective students in this field and bolstering training mechanisms to prepare the workforce.

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⁹ See Chapter 6 for supporting text.

¹⁰ See Chapter 6 for supporting text.

Recommendation 6-2: Universities, technical schools, apprenticeship programs, and states should work toward implementing well plugging and abandonment-specific training and certification programs. These programs should include curricula that prepare current students for using new technologies such as artificial intelligence, provide ways for those currently in the workforce to access upskilling or reskilling, and provide certifications recognized by the industry.

A PATHWAY FORWARD

Tackling the orphan well problem requires long-term planning and resource allocation. State regulatory programs have decades of experience effectively addressing the technical and operational aspects of plugging and remediating orphan wells. Substantial progress has been achieved, and the current momentum, supported by federal funding available through 2030, creates a timely opportunity to significantly increase the number of wells plugged and to enhance the quality and durability of plugging materials and practices. These actions will improve air and water quality and reduce methane emissions.

The committee supports states’ authority to establish their own standards and procedures. Although this approach results in a heterogeneous regulatory landscape, state programs share a commitment to resource conservation and to environmental stewardship, as articulated in the founding principles of the IOGCC. Allowing a heterogeneous landscape allows states to tailor solutions to their specific geologic and technical challenges—such as well history, geology, and other differences in hydrocarbon production.

With the states continuing to lead the work of plugging orphan wells, implementing many of the committee’s conclusions and recommendations will require coordination among many groups: states, federal agencies involved in well plugging and plugging research, Tribes, plugging contractors, industry stakeholders, and non-governmental organizations.