"In order to complete an economic study of UCG, a preliminary design must be made for the process. The design and economic study both require the estimation of a considerable number of variables such as depth and thickness of the coal seam, well spacing, gas heating value and production rate, air injection requirements, well spacing, percentage coal recovery, thermal efficiency of the process, and rate of advance of the gasification zone. Almost never will sufficient experimental data be available to determine all variables with confidence. Furthermore, not all of the variables cited are independent of each other. The purpose of this paper is to show how mathematical models and laboratory data can lead to a major reduction in uncertainties resulting from assumptions associated with economic analyses of UCG. An economic analysis is used to illustrate this method. Mathematical model calculations are used to establish the relationships between variables such as the gas heating value and thermal efficiency. The actual correlations are developed from operating data from the Hanna field tests, but model calculations provide the theoretical explanation for the shape and sensitivity of the experimental curves. Model calculations also allow confident interpolation and extrapolation of the experimental data. The end result is an economic analysis with improved accuracy and few assumptions. Finally, it is shown how economic studies can provide valuable feedback for an ongoing research program. Certain variables have yet to be fully determined such as maximum well spacing , probable gas leakage due to subsidence and long term average gas heating value. Economic studies show which of these variables have the greatest economic impact. Those variables with maximum impact should receive the greatest emphasis in research."