A cognitive task analysis of reliability coordinators in an electric power system control center was performed in conjunction with evaluation of three novel display solutions for line overload detection and correction. Eight experienced regional operations center operators participated in the study. The operators were shown two different geographic data view displays and a tabular, text-based tool, and interviewed as they solved three different transmission line overload problems using the different displays and tools. The operators were asked to think aloud as they performed the tasks. Their comments were recorded and transcribed, and used as a basis for the cognitive task analysis. The results indicated that although the operators liked the system data visualization approaches, they also placed high value on tabular presentation of textbased and numerical data. Visualization solutions should therefore be used to supplement existing displays and tools. This study also serves as an example of a participatory design approach to development of novel visualization solutions for complex task environments.