Lori
If you have a guess at the name of the relative you inherited from, if you post it here someone might be able to help you research the Howard County deed records using TexasFile or one of the other free deed index sites.
You might be interest in this link to recent comments in another part of the forum by someone who was in a similar situation, just a different County, and surprised by a lease offer rather than a purchase proposal.
https://www.mineralrightsforum.com/t/i-inherited-mineral-rights-and-have-questions/61558/36?u=dusty1