Unrecorded Oil and Gas Lease (Lessee is ExxonMobil Corp.)

[John Livingston Bullier]

Hey BP!

I'm representing a buyer who is in contract to purchase a property that is subject to an oil and gas lease to ExxonMobil recorded in 1974. 

The kicker? The lease itself was not recorded, only a "Memorandum" (which lays out the parties to the lease), the legal description of the property, and the notary block. The "Memorandum" references "that certain oil and gas lease made and entered into this day" but it does not include any terms, provisions, expiration date, etc. 

The Lessee is Mobil Oil Corporation of New York....

If it is still in effect I want to get it removed but I don't even know where to start trying to track down the lease. Any thoughts?