Results of two studies concerning contamination from organic compounds in three-phase aquatic microcosm (TPAM) demonstrate the reliability, sensitivity, versatility, and high degree of control the TPAM research technique offers. Benz(a)anthracene (BA) had no detectable effect on the structure or function of an ecosystem simulating Lake Powell, UT/AZ. The fate of over 95% of the compound was known following the 60-day experiment. The majority of BA remained associated with sediments, as predicted based on other studies. In the second study, crude oil addition had a significant impact on microcosms representing Bear Lake, UT/ID, as shown by essentially every parameter measured. Results of the TPAM research were similar to published results of other research, and to related in situ research conducted concurrently. Aspects of the physical environment were apparently the most critical characteristics of the natural system not simulated in the TPAM. Specifically, reduced light intensity during the BA experiment led to some predictably different results than reported for environments in natural systems.