The US Supreme Court has ruled about half of Oklahoma belongs to Native Americans, in a landmark case that also quashed a child rape conviction.
The justices decided 5-4 that an eastern chunk of the state, including its second-biggest city, Tulsa, should be recognised as part of a reservation.
Jimcy McGirt, who was convicted in 1997 of raping a girl, brought the case.
He cited the historical claim of the Muscogee (Creek) Nation to the land where the assault occurred.
The ruling means some tribe members found guilty in state courts for offences committed on the land at issue can now challenge their convictions.
Only federal prosecutors will have the power to criminally prosecute Native Americans accused of crimes in the area.
Tribe members who live within the boundaries may also be exempt from state taxes, according to Reuters news agency.
Some 1.8 million people – of whom about 15% are Native American – live on the land, which spans three million acres.