To gauge the reaction of visitors to various fee levels, Rivera-Planter and Munoz-Pina (2005) carried out a contingent valuation survey and constructed aggregate demand for several parks. They explored the benefits and costs of differentiating fees, looking at both revenue maximising and welfare maximising fees. In Cancun, for example, during the high season, revenue maximising fees would be as high as USD 36 for a foreign visitor and USD 20 for a Mexican visitor (see also Section 4.3).