You and your ex husband can agree to divide the rights between you, equally I am assuming.  I am just concerned about how things may read in the divorce agreement.  I would want you to take the agreement to someone to read to make sure that the matter was not covered in some way (I know that you say that it was not but really someone needs to read i to make sure).  Then you can amend the agreement and agree to divide the rights between you.  Procedurally, however, you may have to go before the court that issued the divorce, as it was an asset of the marriage that was not addressed before. At this point in time it is really just a business arrangement but I would double check on it anyway.  Perhaps call the attorney who handled the divorce for you in the first place.  And call the company who has the drilling rights and ask them what they need to send separate checks.  Good luck.