In Sohio Petroleum Co. v. Grynberg, 757 P2d 1125, 1126 [Colo Ct, App Div I 1988], the court was presented with a top lease with a surrender clause. "A top lease is a lease granted by a landowner, during the existence of a recorded mineral lease, which is to become effective if and when the existing lease expires or is terminated." Sohio, 757 P2d at 1126.) The top lease did not reference the payment of bonus consideration. Rather, the bonus consideration was set forth in letters, which bore no indication that the bonus consideration would be reduced if the lessee surrendered acreage covered by the top lease. (Id.) The lessee in Sohio surrendered a portion of the covered acreage, and paid a bonus to lessor for the acreage retained only. Id. at 1127.) The court in Sohio affirmed a lower court ruling that the lessee "was obligated to pay the entire bonus notwithstanding his release of a portion of the leased premises" before the effective date of the contract." (Id.)