A transfer-on-death deed
An owner can record a deed that names who gets the land when they die. Oklahoma law calls this the Nontestamentary Transfer of Property Act (Title 58, Sections 1251 to 1258). The person named doesn't have to sign anything while the owner is alive.
After the death, each person named signs an affidavit and records it, with a copy of the death certificate, at the county clerk's office where the land sits. For a death on or after November 1, 2011, the law says this has to be recorded within nine months. If it isn't, the land goes back into the estate.
To see whether one was recorded, search the county's land records. In Creek County that's creekcountyland.com.