"Organic compounds released to the environment by hydrocarbon extraction/conversion processes (i.e., synfuel and enhanced oil recovery processes) could be major contributors to the growing problem of ground water contamination. This could be a major problem for a fully developed commercial-scale synfuels industry. One of the least understood, but potentially most important, processes affecting ground water quality is subsurface biodegradation of chemical contaminants. This report summarizes the current state of knowledge on in-situ biodegradation of groundwater contaminants, points out the limitations of current research, and makes recommendations for future research. The sparse literature on the fates of organic contaminants in the subsurface environment provides few, well-documented descriptions of in-situ transformations of organic compounds by indigenous microbiota. In-situ restoration of contaminated aquifers through enhancement of naturally occurring biodegradation processes, however, shows definite promise as an economical means of removing contaminants from the groundwater environment. In contrast, the effectiveness of purposeful introduction of specially adapted or genetically engineered microorganisms remains purely conjectural. To obtain a better understanding of the processes controlling the in-situ fates of organic contaminants, future research should emphasize definitive experimental controls, reliable and extensive sampling of both the microbiota and the parent contaminant or metabolites, increased authenticity in laboratory simulation experiments, and integration of concomitant laboratory and field studies. Only after a dramatic increase in funding to implement these recommendations, can the research community expect to make reliable predictions of the fates of groundwater contaminants and design appropriate aquifer-restoration schemes."