The tax office can be contacted and research done to determine if the mineral owners are being taxed on producing hydrocarbons. If so, it stands to reason that there is currently production on the subject tract. Drive around the area looking for wellheads or pump-jacks that appear to be in the proposed lease play. Plot them on the map and see where they fall. Once the Lessors have been identified, the last thing left to do is phone them to be sure that there is not an unrecorded current lease and that they would be willing to lease their land for exploration.
Most people are willing to talk about an oil lease.
There is something about easy money that softens even the most savage landowner. If you are having problems printing this article, click on a portion of the text of the document.