An expert system based consultant has been developed to assist power system operators in scheduling the operation of generating units. First, problems with existing unit commitment algorithms were identified. Then the knowledge of an experienced power system operator and a unit commitment programming expert were combined to create an expert system rule base. To use the expert system as a unit commitment consultant the operator provides information in response to questions. The expert system uses this information along with the rules either to ask for more information or to reach a conclusion. The expert system answers the most frequent questions raised by system operators and improves the unit commitment solution results by indicating how to adjust input data. It includes the operational constraints not Included in the unit commitment base algorithm and results in a more efficient program execution. Numerical examples and test results show that this approach can obtain a better and operationally more acceptable unit commitment solution.