Massachusetts environmental officials are wading into a wonky debate around the rules governing a state effort to limit the amount of methane that gas companies can emit from leaks in their pipes.

What’s at stake is whether the state can accurately calculate emissions in the state — and then lower them in line with its ambitious climate commitments.

The Department of Environmental Protection has launched a review of its program that requires the state’s six gas companies to meet annually declining limits on methane emissions, a powerful greenhouse gas estimated to warm the planet at more than 80 times the rate of carbon dioxide in the first 20 years after it’s released.

Since the program took effect in 2018, the gas companies have exceeded that methane limit every year through a legal process that allows them to petition the DEP to tap into a reserve, known as a set-aside, if they surge past the emissions cap. That set-aside, according to DEP, is designed to “address unexpected events affecting the natural gas distribution system,” and the utilities can be fined for noncompliance with the regulation.

The program review is opening up a clash between environmental groups, the state attorney general’s office, and the gas companies over the program’s future as the Bay State’s commitment to cut climate warming pollution in half by 2030 compared to 1990 levels appears increasingly in jeopardy.

DEP records show that the gas companies, mainly National Grid and Eversource, have consistently applied for and received approval from state regulators to exceed the methane limit and legally emit more through the set-aside each year since 2018.

For instance, the gas companies together emitted around 147,000 metric tons of pollution in 2024, above the limit of around 140,000 metric tons because DEP approved the utilities’ petition to emit 7,813 metric tons through the set-aside. Eversource’s EGMA subsidiary was responsible for a little more than half of the pollution authorized through the set-aside that year.

What’s more, the amount of methane that the gas companies are emitting beyond the annual cap is growing: The utilities have successfully petitioned to emit more methane through the reserve each year from 2021 to 2024. The 7,813 metric tons of pollution allowed through the set-aside in 2024 is the most since the program began in 2018.

Still, overall methane emissions have declined nearly 13 percent in that timeframe and the companies have never exceeded the state’s maximum annual emissions limit that combines both the standard cap and the set-aside amount — leaving the utilities fully in compliance with the program in spite of their increased use of the set-aside.

Now, as the state looks to accelerate its transition off gas, regulators are openly weighing in their program review what is the appropriate size of the set-aside, as well as where they should set the overall methane emissions caps for the coming years.