"Underground coal gasification (UCG) is a promising way to recover the energy content of one of the United States'most abundant resources. Water influx is a very important factor affecting the UCG process. Little has been achieved to date in identifying, understanding, and modeling water influx. Three principal mechanisms of water influx are identified, described, and modeled in this thesis, in the context of the forward-burn phase of a horizontal-seam, linked vertical Hell UCG process. These components are linked to a cavity-growth model to create a comprehensive, predictive, water-influx model."