An estate in land that automatically terminates if a stated condition occurs. Fee simple determinable estates are followed by a future estate called a possibility of reverter. For example, A conveys land to B "for as long as oil and gas are produced in paying quantities." B has a fee simple determinable and holds the land for as long as oil and gas are produced in paying quantities and A has a possibility of reverter. If the land stops producing oil and gas, the land is automatically transferred back to A.