A practical criterion for the success of a knowledge-based problem-solving system is its usefulness as a tool to those working in its specialized domain of expertise. Here we describe an application of the Prospector consultation system to the task of estimating the favorability of several test regions for occurrence of uranium deposits. This pilot study was conducted for the National Uranium Resource Estimate program of the U.S. Department of Energy. For credibility, the study was preceded by a performance evaluation of the relevant portion of Prospector’s knowledge base, which showed that Prospector’s conclusions agreed very closely with those of the model designer over a broad range of conditions and levels of detail. We comment on characteristics of the Prospector system that are relevant to the issue of inducing geologists to use the system.