43 C.F.R. § 3181.3
The owners of any right, title, or interest in the oil and gas deposits to be unitized are regarded as proper parties to a proposed agreement. All such parties must be invited to join the agreement. If any party fails or refuses to join the agreement, the proponent of the agreement, at the time it is filed for approval, must submit evidence of reasonable effort made to obtain joinder of such party and, when requested, the reasons for such nonjoinders. The address of each signatory party to the agreement should be inserted below the signature. Each signature should be attested by at least one witness if not notarized. The signing parties may execute any number of counterparts of the agreement with the same force and effect as if all parties signed the same document, or may execute a ratification or consent in a separate instrument with like force and effect.
43 C.F.R. § 3181.3