Hi, Dineen -
I agree with Charles Cunningham's suggestion. If a copy of your Divorce Decree and Property Settlement have not already been filed of record in the County where the subject lands are located, then you should do that. If there were any Warranty Deeds or Quitclaim Deeds that were required under the Property Settlement, your Attorney should have already filed those.
It is my understanding that if you each own 1/2 interest in the surface and minerals, then one of you can buy the other out. The selling party can reserve their 1/2 interest in the minerals if they want.
Either that, or you can Partition the land completely, where you get 1/2 of the surface and all of the minerals under your part and he gets 1/2 of the surface and all of the minerals under his part.
Or a hybrid of the two, where the two of you Partition the surface, but with each of you reserving your respective 1/2 mineral interests in the whole.
Unless you give up or have given up the Executive Rights to your minerals (the rights to negotiate and execute documents), he will not be able to leave you out of any future leasing agreements.
You haven't provided any information about your Ownership of the subject property or the terms of your Divorce, but each of yours' interests, both surface and minerals, are more than likely already separate estates.
The Oil and Gas Companies will have to negotiate for leases on the two of yours' interests separately, just as anyone wishing to buy the surface will.
The question of "Why does he want to buy you out?" springs to mind: Does he know something about the future value of the land that you do not? You should be cautious in making any quick decisions to sell until you are fully aware of such things.
Oil and Gas Companies are typically very thorough in their reviews of land and mineral titles. I know from this, because that's the type of work I do for them.
What you really need to do is to speak to an Attorney about things like this. There are too many variables where someone who is not experienced in such matters can wind up being an Unhappy Camper (how's that for PC verbiage?).
If you do not already have an Attorney with experience in both Real Estate and Oil and Gas matters, you are welcome to accept my offer to become "A Friend" on The Forum. As A Friend, I will be able to privately suggest a few that are very experienced in these sorts of matters.
Hope this helps -
Charles Emery Tooke III
Certified Professional Landman
Fort Worth, Texas