If you have several offers in hand, then you already have a general idea of what your particular acreage is worth on the market.
Our attorney said that a “fair” price is what a willing and informed seller under no compulsion to sell and a willing and informed buyer under no compulsion to buy agree to. (Buyers tend to be more informed than mineral owners since they have the geologists, engineers and market knowledge.)
You can also look in the Directories tab above for Pecan Tree appraisers. They have a tool that acts similarly to Zillow for mineral rights to give a reasonable estimate for what the minerals may be worth from a production point of view. It may not be the same range as your offers, but can be helpful.
Buyers generally offer a price that is based upon a certain number of years of production discounted to the time value of money.
Remember that a sale may trigger capital gains, so you need to know your basis and take that into account. And a large sale may bump you into a different tax bracket, so that is another piece of the puzzle.