The size of the protected area is recognized as one of the key attributes for assessing the effectiveness of investing in protected areas. We evaluate the effectiveness of protected areas by examining economies of scale in size and the average cost of acquiring protected areas depending on the land acquisition contract types and motivations. We use recent land acquisitions (2000-2009) of the central and southern Appalachian forest ecosystems by The Nature Conservancy (TNC) as a case study. Our findings suggest that (1) the purchase of protected areas achieves economies of scale in size on average; (2) the fee simple deals achieve economies of scale in size while the easements do not, and the easement deals are more cost effective than the fee simple deals; (3) targeting the protection of mammals or birds achieves greater economies of scale than not targeting them; and (4) the deals without development pressures achieve greater economies of scale in size than the deals with the threat of development. Our findings will help TNC and other conservation organizations to design more cost effective investments in land conservation. Cost effectiveness, Economies of Scale, Land conservation, Protected area size., Environmental Economics and Policy, Land Economics/Use,