Estimating value of mineral interests

We inherited mineral interests in several locations in Pottawatomie Co, OK. The Oklahoma probate is filed, and we are receiving royalties on some of the Division Orders. My question now is what is a fair value for the mineral interests should we decide to sell? I know those that have wells that are producing have more value than those that are not producing. Are there valuation averages for producing and non-producing mineral interests in Pottawatomie Co?