A commonly visualized benefit from natural resources is outdoor recreation including activities such as fishing, hunting, hiking, and nature study. Due to the extra-market nature of these activities, monetary measures of the benefits emanating from them require use of some kind of simulated prices. The procedure most widely used for this purpose has been that of estimating a demand function, using differential travel costs associated with the locational dispersion of the recreationists, as a proxy price variable. These methodologies may be labeled as “willingness to pay” approaches and have been used by a number of economists.