25 CFR § 151.7 - Acquisition of fractional interests.
(a) The buyer already owns a fractional interest in the same parcel of land; or
(b) The interest being acquired by the buyer is in fee status; or
(c) The buyer offers to purchase the remaining undivided trust or restricted interests in the parcel at not less than their fair market value; or
(d) There is a specific law which grants to the particular buyer the right to purchase an undivided interest or interests in trust or restricted land without offering to purchase all of such interests; or
(e) The owner of a majority of the remaining trust or restricted interests in the parcel consent in writing to the acquisition by the buyer.