(CN) – Oil and gas spills related to fracking have occurred far more often than previously reported, and the quagmire of reporting rules state-by-state may be to blame for the discrepancy between reports and reality.

A team of researchers analyzed how variations in state-level spill reporting criteria contribute to uncertainty among industry leaders, policymakers and the public as to the true extent of the problem. Their report was published in the journal Environmental Science & Technology.

“State spill data holds great promise for risk identification and mitigation,” lead author Lauren Patterson said. “However, reporting requirements differ across states, requiring considerable effort to make the data usable for analysis.”

Patterson’s team reviewed spill data from Colorado, New Mexico, Pennsylvania and North Dakota in order to characterize spills associated with the process known as hydraulic fracturing – fracking – at 31,481 oil and gas wells in those states between 2005 and 2014.

North Dakota reported the most spills, with 4,453 incidents, followed by Pennsylvania at 1,293. Colorado reported 476 spills, while New Mexico disclosed 426 spills.

This wide-ranging rate of spills is largely due to varying minimum thresholds for reporting such incidents. North Dakota requires reporting spills of 42 gallons or more, while Colorado and New Mexico only require reports for spills of at least 210 gallons.

Spills include not just oil, but also chemical-laden water and fracking fluid.

“As this form of energy production increases, state efforts to reduce spill risk could benefit from making data more uniform and accessible to better provide stakeholders with important information on where to target efforts for locating and preventing future spills,” Patterson said.

The number of spills identified by the team also exceeds the 457 spills calculated by the U.S. Environmental Protection Agency for eight states between 2006 and 2012. The agency’s estimate only considered the fracking stage, rather than the entire process of unconventional oil and gas production.

“Investigating all stages helps to shed further light on the spills that can occur at all types of wells – not just unconventional ones,” Patterson added.

Half of the spills identified in the new report were related to storage and moving fluids via pipelines, although it was not always possible to determine the cause since reporting data for some states relied on narrative descriptions.

The team found that the first three years of a well’s life – when drilling and fracking production volumes are highest – posed the greatest risk of a spill. The report shows that a large portion of spills, including 53 percent in North Dakota, occur at wells that had more than one spill.

“Writing state reporting rules with these factors in mind is critical, to ensure that the right data are available – and in an accessible format – for industry, states and the research community,” said co-author Kate Konschnik, director of the Harvard Law School’s Environmental Policy Initiative.

“Analyses like this one are so important, to define and mitigate risk to water supplies and human health.”