How to determine "fair market value" of mineral rights

How many acres do you own? If it’s not many and they aren’t leased, and don’t have offers, I think a few hundred bucks an acre would be pushing it when it comes to value. But I could be wrong. Have you ever leased it within last 5 years? If so, value it at 3x that amount. They say a good rule of thumb is that they are worth 3x the going lease rate.