Three demand systems were estimated to examine demand sensitivity and welfare changes for each commodity under study. In the first essay, a Quadratic Almost Ideal Demand System (QUAIDS) was used to examine the effect of the Fukushima Daichi nuclear disaster on the demand for imported pelagic fish in the domestic Japanese market. The effect of the Fukushima Daichi nuclear disaster was measured using changes in demand after the disaster as well as measures of changes in social welfare changes caused by the disaster. A significant effect of the disaster on demand sensitivity measures was found, but no significant changes in welfare. In the second essay, a differential demand system examined the effect of exchange rate fluctuations on the demand for fresh tomatoes in the U.S. Market. It was found that the U.S. Dollar-Mexican Peso exchange rate had a significant positive effect on the demand for Mexican fresh tomatoes. In the third essay, a Hurdle Negative Binomial demand system was estimated for recreational trips to the Boundary Waters Canoe Area Wilderness. This model was estimated using Bayesian methods to obtain parameter estimates that could not be obtained by maximum likelihood. The parameters were used to calculate recreational welfare measures for trips to seventy-two entry points.