It’s no secret that oil and gas companies are on the hunt for new places to drill. But the quest for more fossil fuels could heat up in places you might not expect: our national parks.

With President Donald Trump’s executive order on energy, federal agencies are now reviewing all rules that inhibit domestic energy production. And that includes regulations around drilling in national parks that, if overturned, could give oil and gas companies easier access to leases on federal lands they’ve long coveted.

"This opportunity is unique, maybe once in a lifetime," Jack Gerard, president of the American Petroleum Institute lobby group, told Reuters. It could also put some of America’s most pristine and ecologically sensitive areas at risk of oil spills, ground contamination, and explosions.

There are currently more than 500 active oil and gas wells spread across 12 national parks, as you can see in the map below. In 2015, drilling on federal lands made up nearly a fifth of overall US production.

Meet the 9B regulations: rules that allow companies to drill for oil and gas in national parks

If you’re wondering why it’s legal to drill in national parks in the first place, it’s due to a little-known set of rules called the “9B regulations.”

Introduced in 1978, the 9B rules manage issues of “split estate,” or instances where the federal government owns the surface land but private individuals and companies own the mineral rights below ground. As Nicholas Lund, a senior manager at the National Parks Conservation Association, told Vox, these well rights often predate the parks.

“A lot of the reasons these wells exist is because when the federal government purchased the park, they weren’t able to obtain the well,” he said. “Either the owners refused to sell them the subservice area or the government set park boundaries that included oil and gas in it.”

The rules were last updated in 2016 and include a number of basic safety and environmental measures to mitigate the impact of drilling in national parks. For instance, companies must use minimally invasive drilling practices, submit plans to the Park Service for review, and set aside funds to clean up an area after drilling is finished.

But now, under the Trump administration, those safeguards are at risk of being watered down or repealed, shifting the burden to protect national parks to environmental watchdogs. And 30 additional national parks with split estate situations could be opened for drilling in the future.

According to the NPCA, split estate “presents a potential for conflict when a private company exercises its rights to extract minerals while the National Park Service tries to uphold its legal mandate to leave parks ‘unimpaired for the enjoyment of future generations.’”

Environmental groups fear that parks located in oil and gas hot spots are easy targets for increased drilling under President Trump

There are 30 parks where drilling could now happen under Trump’s executive order, but environmental groups are particularly worried about a handful of parks located in drilling hot spots.

Big Cypress National Preserve, 45 miles west of Miami, is a national park in southwest Florida home to a variety of critically endangered species including the Florida panther, the red-cockaded woodpecker, and the West Indian manatee.

Data from FracTracker Alliance, which collects information on the more than 1.7 million oil and gas wells in the US, shows there are already 20 active oil and gas wells in the preserve. But the Collier family, which owns the mineral rights beneath nearly 400,000 acres in Big Cypress, is now looking to expand operations.

In May, NPS ruled that Burnett Oil Co., which leases rights from the Colliers, could explore for oil and gas in 70,000 acres of the preserve. But six environmental groups filed a lawsuit last July to stop the exploration, citing concerns that seismic testing would disrupt wildlife, kill vegetation, and erode soils in this fragile area. (The lawsuit is still being fought in federal court.)

If the 9B regulations on drilling for oil and gas are relaxed, environmental groups fear that exploration for new wells will undergo less scrutiny and could even be fast-tracked in parks like Big Cypress.

It could also lead to oil and gas exploration in the neighboring Everglades National Park. Everglades National Park does not currently have any active oil or gas wells, but it is one of the 30 national parks with split estate agreements.

National parks in New Mexico and Pennsylvania might start drilling next because of their proximity to existing oil and gas operations.

Other parks located in areas that are already drilling hotbeds — like Carlsbad Caverns National Park in New Mexico and Friendship Hill National Historic Site in Pennsylvania — could also be some of the first parks to allow drill under the new administration.

Why? As you can see in the maps below, these two places are already surrounded by a number of active oil and gas wells. According to Lund, this might embolden landowners to exercise their mineral rights if these rules are repealed or weakened.

“When you look at [data from] FracTracker, you can see that a park like Carlsbad Caverns is surrounded by huge fields of oil and gas,” said Lund. “There is going to be pressure in some of these places to drill.”

On the other hand, Lund told me that parks like Grand Teton in Wyoming and Indiana Dunes National Lakeshore are less at risk because they aren’t surrounded by intense oil and gas development.

But given that national parks protect some of America’s most unique and fragile ecosystems, any new drilling for oil and gas risks disrupting habitats and polluting what little of America’s untouched wilderness is left.