XML-based interchange formats for performance models provide a mechanism whereby performance model information may be transferred among modeling tools. For example, the PMIF allows diverse tools to exchange queueing network model information. Formats have also been defined for the interchange of LQN, UML, Petri Nets, and others. These formats specify the model and a set of parameters for one run. For model studies, however, it is useful to be able to specify multiple runs, or experiments, for the model. This paper presents an XML interchange schema extension for defining a set of model runs and the output desired from them. It has the expressive power to specify iterations, alternations, assignments of values, actions based on model results and more. Examples illustrate how the experiment interchange extension can be used with a wide variety of performance modeling paradigms. A prototype proves the concept.