In the United States, oil and gas rights to a particular parcel may be owned by private individuals, corporations, Indian tribes, or by local, state, or federal governments. Oil and gas rights extend vertically downward from the property line. Unless explicitly separated by a deed, oil and gas rights are owned by the surface landowner. Once severed from surface ownership, oil and gas rights may be bought, sold, or transferred, like other real estate property. Ownership in the oil and gas rights for different horizontal layers, or strata, may be further divided and sold to different parties.