You need to research to see what fractional interest you have acquired, whether by purchase or by inheritance. First, look at your deed(s) to see the legal description which should list the section, block, survey and gross acres in which you own an interest. You will then need to search “backwards” in time through the deed records to see what your predecessors owned. For example, if you deed is from your father John, then you look for the earlier deed from X into John. Then you look back farther for the deed from A into X. Your question is to determine if you and your siblings own 100% of the gross acres or only a combined fraction. Suppose X deeded 1/2 of 200 acres to John and 1/2 to Mary, and then John deeded his interest to you. Then you own a combined 1/2 of 200 acres, which is described as 100 net mineral acres. But suppose that A had deeded 1/2 to X and 1/2 to Y. Then when X deeded 1/2 to John, John only got 1/4 (that is 1/2 of 1/2). It can be a process to research the deeds. Pecos County deeds can be found on TexasFile.com back to 1911. You can look for free, but need to pay for copies. It it worthwhile to have the deeds in a file. If your minerals are producing, then you can ask the operator for the part of the Drilling Title Opinion which states what you own. This will not give you the title history and only give you the fractional interest in the gross acres in the tract. If you own an NPRI, then that interest will be described somewhere in the deed history as a reservation out of a grant of minerals. You can also hire a landman to do this research for you. Be sure to get the deed references and get copies of the deeds. It is important for you to determine what you own so that you are paid correctly for lease bonus and royalties.