I can't speak to what the going rate is for leases or mineral sales in Kingfisher County. But I can say that given the very small size of your interests, and the problems you may have because of the lack of formal transfers, selling may be a good way to go for you. Owning mineral interests properly can be a lot of work and requires a lot of knowledge and experience to be done right. I don't see 0.6 acres being worth the time and headaches it would take to keep them. If you do decide to sell, you should solicit multiple offers to get the best value.