Sparky:
Establishing a value on minerals is not an easy task. You have to consider your total net mineral acres in an area, how close is a producing well to your minerals and what is the production, what is the current bonus rates for your area in regards to leasing and is your area currently leased and on what terms. I would avoid seeking a formal appraisal if possible due to the extra expense and most likely they will utilize these same methods in determining the values.