Last November, the Ninth Circuit Court of Appeals vacated a US government decision allowing Shell Oil Co. to explore for petroleum north of Alaska. On 6 March, the same court vacated its own decision, leaving everybody scratching their heads.

The original decision ordered the Minerals Management Service (MMS) to redo its analysis of environmental and cultural impacts of oil development. Unfortunately, the one-paragraph ruling issued this month didn’t offer any other details, except to say that a new decision would be forthcoming at an unspecified date.

MMS opened up new territory in the Beaufort Sea to leasing several years ago, although environmental groups have been fighting the development each step of the way. Reuters reports that Shell Oil spent US$83.7 million on MMS lease sales in 2005 and 2008, along with US$2.1 billion on leases in the nearby Chukchi Sea.

What happens next is anybody’s guest. Shell had initially planned to begin its exploration program in 2007, but the ongoing legal battle has pushed that off until at least 2010, depending on what eventually comes out of the Ninth Circuit.