Federal officials have not inspected more than half of the thousands of oil and gas wells designated as "high priority," an investigation from the Government Accountability Office (GAO) said Monday.

The new report found that the Bureau of Land Management (BLM), which has authority to inspect oil and gas exploration leases on federal and American Indian land, identified 3,702 wells drilled from 2009 to 2012 as high-priority for geological reasons, such as proximity to usable water or high-pressure zones. But the agency failed to inspect more than 2,100 of those wells.

Furthermore, the GAO, said, due to overlapping authorities, some wells get duplicative inspections by state officials and the BLM, which part of the Interior Department.

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“BLM officials told us that the agency has limited staff to complete drilling inspections, which is consistent with our prior report stating that Interior’s human capital challenges have made it more difficult to carry out some oversight activities and that the agency conducted fewer inspections because of inspector vacancies,” said the report released Monday.

The investigation faulted the bureau for a wide variety of other shortcomings in its oversight of oil and gas wells.

At the same time, domestic oil and gas production has reached historically high levels, due largely to hydraulic fracturing, also known as fracking.

The GAO said the agency’s policies for approving or recommending leases rely on outdated science and come from a time before fracking and other nontraditional techniques were as common as they are now.

“The agency cannot accurately and efficiently identify whether federal and Indian resources are properly protected or that federal and Indian resources are at risk of being extracted without agency approval,” the GAO report said.

The BLM has proposed updates to its regulations to account for fracking, and officials told the GAO those rules would likely be in place by 2015.

The investigation found that the duplicative inspections were mostly due to a lack of coordination with state officials. States can inspect wells on any land within their borders, including federal and Native American land.

So far, the BLM has only reached coordination agreements with California, Colorado, Nevada and Wyoming, and the report urges the agency to seek similar pacts with other states.

Tommy Beaudreau, principal deputy assistant secretary of Interior, said his department concurred with the GAO report. Interior department officials declined to comment further to The Hill.

The report came less than a month after the Congressional Research Service found that oil production fell 6 percent and gas production dropped 28 percent on federal land between 2009 and 2013. In that same time, oil production grew 61 percent and gas production rose 33 percent on nonfederal land. Republicans blamed President Obama's energy and land use policies for the decreases.