JUNEAU, Alaska (AP) — An appeals court panel is deciding whether to let stand the Biden administration’s approval of the massive Willow oil project in a federal petroleum reserve on Alaska’s North Slope.

Environmentalists and a grassroots group called Sovereign Iñupiat for a Living Arctic are seeking to have last March’s approval overturned. Arguments before a 9th U.S. Circuit Court of Appeals panel Monday in San Francisco focused largely on the groups’ claims that the U.S. Bureau of Land Management did not consider a “reasonable” range of alternatives in its review and limited its consideration of alternatives to those that allowed for full-field development of the project by ConocoPhillips Alaska.

The court did not immediately rule.

Amy Collier, a U.S. Justice Department attorney, told the court the federal agencies involved complied with their legal obligations. Jason Morgan, an attorney for ConocoPhillips Alaska, said Willow wasn’t presented on a “blank slate” — that prior lease decisions providing a right to develop subject to restrictions and a plan governing where development in the National Petroleum Reserve-Alaska can take place also were part of the equation.

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“Context is very important,” Morgan said.

In court documents, he and other attorneys for the company said the leases in ConocoPhillips’ Bear Tooth Unit are in areas open to leasing and surface development and that the Bureau of Land Management committed the unit to development in issuing leases there over a period of years. Willow is in the unit, in the northeast part of the petroleum reserve.

Two separate lawsuits seek to overturn the project’s approval. A coalition of environmentalists in one of the cases argues the Bureau of Land Management predicated its assessment “on the flawed premise that it must allow ConocoPhillips to extract all economically viable oil from its leases and assessed only a narrow range of action alternatives that each allowed nearly identical oil production.”

The groups are challenging U.S. District Court Judge Sharon Gleason’s decision in November upholding Willow’s approval. She found ConocoPhillips Alaska has the right to develop its leases in the reserve “subject to reasonable restrictions and mitigation measures imposed by the federal government.” She found the Bureau of Land Management “did consider the requisite reasonable range of alternatives based on the Project’s purpose and need.”

Work on the project is underway after Gleason and an appeals court rejected efforts by the environmental groups to block winter activities, including construction of new gravel roads, while the appeals are being heard.

State political and union leaders have endorsed Willow, and the project has broad support among Alaska Native leaders on the North Slope and groups with ties to the region who see Willow as economically vital for their communities.

Climate activists see the project at odds with President Joe Biden’s pledges to combat climate change. The administration has defended its climate record.

It is estimated that using the oil from Willow would produce the equivalent of about 263 million tons (239 million metric tons) of greenhouse gases over the project’s 30-year life, roughly equal to the combined emissions from 1.7 million passenger cars over the same time period.

ConocoPhillips Alaska proposed five drilling sites for Willow but the bureau approved three, which it said would include up to 199 total wells. The project could produce up to 180,000 barrels of oil a day at its peak. Supporters say that would be significant for the trans-Alaska pipeline, which hit its peak for throughput in 1988 with an average of about 2 million barrels per day.

An average of about 470,000 barrels a day coursed through the pipeline last year.