Mixing has been the focal point of many experimental studies in recent years, but advances in modeling and simulation now allow for fast, accurate and useful simulation analysis. Numerous mixing indices have been developed but the majority are tailored to experimental studies. lit this study, a new mixing index is developed to analyze the particle position history of the mixer. Due to its simplicity when dealing with moving boundary problems, the boundary element method is employed to model the fluid flow and track particles. Numerous geometries can be modeled and compared on a basic workstation. First the mixing index is applied to Couette flow. Analytical and boundary element simulation results compare well. Next the method is used to analyze the mixing capabilities of a Banbury mixer with different speed ratios. Further the mixing index is used to compare the mixing capabilities of triangular mixing lobes versus typical Banbury type.