JUNEAU, Alaska (AP) -- A federal appeals court panel on Friday refused to overturn the approval of the massive Willow oil project on Alaska's petroleum-rich North Slope.

The decision from a panel of the 9th U.S. Circuit Court of Appeals comes in a long-running dispute over the project, which was greenlit in March 2023 by then-President Joe Biden's administration and is being developed in the National Petroleum Reserve-Alaska by ConocoPhillips Alaska.

The court's majority opinion found what it called a procedural but not substantive error by the U.S. Bureau of Land Management as part of the analysis in approving Willow. The majority determined that overturning the project's approval would be unwarranted and its consequences severe.

During the cold-weather seasons, ConocoPhillips Alaska has worked to build infrastructure such as new gravel roads, bridges and pipelines at the project site.

The ruling comes more than a year after the appeals court panel heard arguments in the case. Environmentalists and a grassroots Iñupiat group had appealed a lower-court ruling that upheld Willow's approval.

Alaska's Republican governor and members of its congressional delegation and state Legislature have backed Willow. The project also 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.

J. Elizabeth Peace, a spokesperson with the U.S. Department of the Interior, said the agency doesn't comment on litigation. The Bureau of Land Management falls under the Interior.

Messages seeking comment were left with ConocoPhillips Alaska and environmental groups.