The Environmental Defense Fund (EDF) released an analysis this week that claims, “Pennsylvania’s oil and gas companies emit at least five-times more methane pollution than they report to the state.” But EDF’s analysis is misleading, considering it’s based on an outdated report that overestimated emissions and the fact that only the unconventional oil and gas industry – which represents 82 percent of new wells drilled since 2015 and 72 percent of the wells drilled in 2015 – is required to report emissions to the Pennsylvania Department of Environmental Protection (DEP). The unconventional industry is also the only industry that is targeted by the new proposed methane emissions regulations.

The latter said, it is far more relevant that Pennsylvania’s unconventional oil and gas industry has been steadily reducing its methane emissions since reporting began in 2012, and recent sampling has shown that methane leakages rates in the Marcellus are “very low.” That’s significant, considering the unconventional industry represented a mere 18 percent of new wells drilled from 2000 to 2015 before jumping to 82 percent from 2015 to 2018, with production skyrocketing to more than five trillion cubic feet of natural gas annually.

Based on Outdated Study That Overestimated Emissions

EDF’s “five-times more methane pollution” topline conclusion is based on the findings of a 2016 study (Omara et al.) that sampled 35 conventional and unconventional well sites in West Virginia and Pennsylvania in 2014 and 2015. Importantly, Omara et al. is actually part of a larger federally-funded study (Presto et al.) that began in the Marcellus and eventually was expanded to include several basins across the country. That more recent and comprehensive study found that methane emission estimates for Pennsylvania and West Virginia were actually 40 percent lower than those reported in Omara et al. — the study EDF bases its estimates off of – due to “improved statistical power in the current study and methodological differences in the treatment of high emitting sites.”

Specifically, the more comprehensive 2017 study found,

“From the 511,000 O&G production sites, we estimated total U.S. onshore CH4 emissions of 700,000 kg/h (or 6.1 million metric tons) in 2015. These CH4 emissions were equivalent to 1.43% of total CH4 production in 2015, or 1.6 kg/h/site.” (emphasis added)

Notably, the lead author of the 2016 study EDF used for this analysis, Mark Omara, left for a job at none other than EDF before the 2017 study was released.

Methane Leakage Rates Are Low

The more comprehensive 2017 study also determined that 2015 methane emissions leakage rates in both the southwestern and northeastern parts of the state were less than one percent of production. This is significant for a variety of reasons, the biggest being that in order for natural gas to maintain its climate benefits methane leakage rates have to fall below 3.2 percent – and they are well below that rate in Pennsylvania. Importantly, the leakage rate estimate from the more recent and comprehensive 2017 study includes conventional sites (i.e. generally older equipment) and wells from the southwestern portion of the state where the gas is “wet,” meaning there are more natural gas liquids (NGLs) and thus more equipment on site (i.e. more opportunity for leaks). Still, the study found leakage rates well below one percent of production.

Penn State University also released a Department of Energy-funded study in 2017 that found that leakage from wells and related infrastructure in the northeastern part of the state are roughly 0.4 percent of production, which the researchers noted is “significantly lower than rates found using top-down methodology at any other basin.”

And this wasn’t the typical one- to two-day flyover study. Instead, researchers gathered samples from stationary towers over a two-year period and performed a series of 12 aerial flyovers in May 2015 to reach their conclusions. From the study:

“Using the model optimization technique presented in this study, we find a weighted mean natural gas emission rate from unconventional production and gathering facilities of 0.36% of production with a 2σ confidence interval from 0.27 to 0.45% of production. This emission rate is supported by four mass balance calculations, which produce a mean of 0.40% and a 2σ confidence interval of 0.08–0.72% of production. Applied to all the wells in our study region, this mean rate results in a leakage rate of 20MgCH4 h−1 for the year 2015.” (page 23, emphasis added)

Numerous other EDF studies — including this report, which finds the average loss rate for unconventional wells was 0.27 percent — have found low methane leakage rates. In fact, EDF released nearly a dozen studies in 2015 (three of which are included in the graphic below), which found leakage rates of between 1.2 and 1.9 percent.

Methane Emissions Continue to Decline

As Marcellus Shale Coalition (MSC) president David Spigelmyer explained in July 2017,

“As a result of a collaborative effort between industry and regulators, Pennsylvania already has an effective program in place addressing methane emissions that requires operators to follow strict leak detection, repair and reporting requirements.”

And as MSC’s fact sheet on methane explains, some of the specific actions that have been taken in the Marcellus include:

  • “Eliminating venting and flaring by directing the gas that flows back during well completion activities directly into pipelines.”
  • “Using vapor recovery systems, collecting vapors from dehydrators, water trucks and tanks.”
  • “Using air instead of gas for pumps and pneumatic controllers.”
  • “Using Leak Detection and Repair (LDAR) equipment to identify and eliminate leaks.”

The results of these initiatives have been notable. EDF doesn’t provide estimates for years prior to 2015, but unconventional industry methane emissions dropped by 8.5 percent in Pennsylvania from 2012 to 2015, based on DEP’s “2015 Air Emissions Inventory for Unconventional Natural Gas Operations.”

As DEP explained,

“The average emission per well site was 8.3 tons in 2012 and 5.8 tons in 2015. Year to year changes in other emissions are related to a variety of factors, including where wells are drilled and types of equipment being used.” (emphasis added)

That’s a 30 percent average emissions reduction at well sites and a 59 percent reduction in methane emissions per unit of production (one million cubic feet of natural gas) from 2012 to 2015.

Pennsylvania Follows Trend of Declining Oil and Gas Methane Emissions Throughout the U.S.

This trend of declining oil and gas methane emissions isn’t just occurring in Pennsylvania, either. U.S. natural gas system methane emissions have declined 16.3 percent since 1990 at the same time natural gas production has increased 50 percent. New research from the Gas Technology Institute’s Center for Methane Research also shows that methane emissions from the U.S. natural gas industry account for just 1.2 percent of 2016 global methane emissions and 0.2 percent of total radiative forcing. In other words, U.S. natural gas methane emissions have an infinitesimal impact on global warming.


The DEP’s annual emissions inventory makes it very clear that the emissions reported are for the unconventional oil and gas industry only, and the industry uses EPA- and DEP-approved methodology to calculate its estimates. But regardless as to whether emissions are closer to what has been reported or EDF’s inflated estimates, it does not change the fact that Pennsylvania’s oil and gas operations have incredibly low methane leakage rates and methane emissions from this sector continue to decline.