The Laboratory has been conducting an interdisciplinary underground coal gasification program since 1974 under the sponsorship of DOE and its predecessors. We completed three UCG tests at the Hoe Creek site near Gillette, Wyoming, during the period 1975 to 1979. Five small field experiments, the large-block tests, were completed from 1981 to 1982 at the exposed coal face in the WIDCO coal mine near Centralia, Washington. A larger test at the same location, the partial-seam CRIP test, was completed during fiscal year 1984. In conjunction with the DOE and an industrial group lead by the Gas Research Institute, we have prepared a preliminary design for a large-scale test at the WIDCO site. The planned test features dual injection and production wells, module interaction, and consumption of 20,000 tons of coal during a hundred-day steam-oxygen gasification. During fiscal year 1984, we documented the large-block excavations. The cavities were elongated, the cavity cross sections were elliptical, and the cavities contained ash and slag at the bottom, char and dried coal above that, and a void at the top. The results from the large-block tests provided enough data to allow us to construct a composite model, CAVSM. Preliminary results from the model agree well with the product-gas chemistry and cavity shape observed in the large-block tests. Other models and techniques developed during the year include a transient, moving-front code, a two-dimensional, reactive-flow code using the method of lines, and a wall-recession-rate model. In addition, we measured the rate of methane decomposition in the hot char bed and developed an engineering rate expression to estimate the magnitude of the methane-decomposition reaction. 16 refs., 30 figs., 1 tab.