The full or partial acquisition of land remains a predominant focus of terrestrial conservation strategies. Non-governmental organizations play an important role in habitat protection, yet few studies investigate their contribution to conservation investment. Here we examine temporal trends in the size of land transactions made by the world's largest land trust, The Nature Conservancy (TNC). We consider three dimensions of deal size (area, upfront cost, and relative cost per hectare) for two commonly used conservation approaches (fee simple acquisitions and conservation easements). Mean area of protected land parcels has been robust to the growing subdivision of properties for sale. Variation in the area and cost of transactions ranged between six and eight orders of magnitude, and increased through time as TNC undertook occasional large deals once established. Conservation planning approaches need to better account for the variation in deal sizes, and how this may change in response to dynamic budgets and priorities.