COOK, Circuit Judge. In 1968, the heirs of J. H. Northup, predecessors in interest to appellant Northup Properties, Inc. (“Northup”), executed an oil-and-gas lease of 4,327 acres in Kentucky (the “Lease”) to United Fuel and Gas Company, the predecessor in interest to appellee Chesapeake Appalachia, L.L.C. (“Chesapeake”). For nearly forty years, no lessee—including Chesapeake—marketed either oil or gas from the leased property. Northup then filed suit in Kentucky state court for a judgment declaring the Lease null and void. Chesapeake removed the case on the basis of diversity jurisdiction, and the two parties filed cross-motions for summary judgment. After a hearing, the district court granted summary judgment for Chesapeake and denied Northup’s motion. Northup appealed, and we affirm.