In situ lignite gasification field tests have been conducted at the Rockdale Test Site by the Petroleum Engineering Department of Texas A and M University. The primary goal of the tests has been the development of technology required to exploit deep-basin lignite resources that are too deep to be mined economically by conventional methods. The objective of the study reported herein was to investigate those geotechnical factors that may influence the performance of in situ gasifiers. Because these geotechnical factors are site specific, the emphasis of this study has been on the in situ gasification trials at the TAMU Rockdale Test Site. The scope of the study included field, laboratory, and numerical modeling tasks related to the role of geotechnical parameters involved in in situ gasification of lignite. Topics included: (1) strength, deformation, permeability, and porosity of lignite and associated overburden materials; (2) regional and local geological structure - particularly orientation of joints and faults and their relationship to strength, deformation, and hydrogeologic parameters; (3) local groundwater hydrology; (4) changes in these parameters resulting from the gasification process; and (5) geophysical methods for cavity detection and monitoring. The results of this study confirm and emphasize the need for adequate pretest baseline data collection and interpretation. Further, it is concluded that anisotropic hydraulic conductivities may be adequately determined by multiple well interference testing and that knowing the preferred directions of flow is important to design of gasification tests. Other conclusions are presented. Primary recommendations are that extensive pretest baseline studies should be run to provide a base for subsequent interpretation of post test results. 88 refs., 19 tabs.