In recent years, increases in the number of visitors to national parks such as Yellowstone and Grand Canyon have resulted in over $12 billion in deferred maintenance costs. In response to the overcrowding that has contributed to the cost overruns, the Park Service has considered limiting the number of daily visits to the parks and soliciting corporate sponsorships. Margaret Walls, a research director and senior fellow at Resources for the Future, has offered another suggestion: Increase entrance fees. But she warned: “Figuring out an efficient and fair fee structure will not be easy. It requires detailed data on visitation, for starters, as well as analysis to shed light on price elasticities of demand for different groups of visitors at different locations.” Why is it important for the Park Service to have estimates of price elasticities of demand before raising entrance fees to the national parks?