Gasification experiments covering a wide range of temperatures (800 to 1400/sup 0/C) and pressures (0 to 200 psig) were conducted at high heating rate (100 to 1000/sup 0/C/sec) for the chars of three American coals, viz., an N.D. lignite, a Washington subbituminous coal and an N.M. bituminous coal, using a unique high temperature/pressure thermal gravimetric analyzer. A significant feature of this project was the gasification of the chars in steam starting directly from coals (thus termed ''in-situ''chars), as opposed to a large number of previous studies in which coals were devolatilized in inert atmosphere before being gasified under totally different environments. For comparison purpose, the latter type of char, designated in this report as ''non-in-situ''or ''nitrogen''char, was also studied together with the ''in-situ''char. For each coal, reactivity, conversion, activation energy, and other kinetic data were determined for both types of char and the results were compared, discussed and correlated. In this work, the method of using half life of reaction to unify coal gasification data was further extended to allow easy estimation of activation energy directly from half life data of the gasification reaction. Models for reactivity and conversion were also developed. In addition, microstructural properties, including specific surface area, of the ''in-situ''chars at different stages of conversion, as well as the ''non-in-situ''chars, were determined by gravimetric adsorption method using CO/sub 2/ at 25/sup 0/C as adsorbate and the results were discussed and interpreted. The surface area data obtained were correlated and models relating surface area and conversion were also developed. 58 refs., 47 figs., 22 tabs.