It all depends on the exact wording of the deed which established the NPRI or mineral interest. Some reserve only a specified royalty decimal (1/32). Some reserve a portion on the negotiated royalty (1/8 of royalty). Generally do not include bonus or delay rentals. Some sell minerals but seller reserves executive right to lease on behalf of buyer, but specify that buyer gets his share of bonus. So you have to go back though all the deeds to determine what you have. There are many variations in language and a lot of court decisions interpreting the meaning.