"The spalling of sidewalls or roofs in underground coal gasification is modeled by assuming that it occurs due to strength reductions caused by heating, drying, or crack formation. The temporal or spatial variations of these effects are determined by the properties which control internal convection, diffusion, and conduction in the coal, liquid, vapor, or gas flows. This paper examines the effects of changing these properties to determine the sensitivity of the regression process. It is found that the drying process is primarily sensitive to the coal thermal conductivity, internal diffusion of vapor and the surface heat transfer coefficient while the regression is dominated by the surface heat transfer coefficient and only slightly affected by the surface resistance to vapor flow."