Mathematical modeling technologies hold promise as an approach for providing training system designers with critical information regarding human behavior in complex systems. Such information is useful in researching training principles, defining instructional strategies, developing performance measures and establishing diagnostic and feedback mechanisms. An area that is particularly complex for training system designers involves multi-operator systems, where an understanding of individual human performance must be augmented by an understanding of team performance and functioning. To date, several approaches have been proposed to model team performance, but further methodological advances are needed. The purpose of this paper is to describe the use of Petri nets, a mathematical modeling technique, as a means to model complex team functioning and as a basis to develop team performance measures.