The PAN AIR program has demonstrated its utility for analyzing complex aircraft configurations at subsonic and supersonic speeds The code, however, has not demonstrated the ability to predict mutual interference effects due to close proximity, particularly at supersonic speeds Comparisons with test data for stores in proximity to a two dimensional flat plate at supersonic speeds have shown that plate modeling, as well as nose bluntness, have a significant impact on the results Comparisons for stores in proximity to axisymmetric bodies indicate that, for three dimensional flowfields, mutual interference effects are better predicted Application of a procedure (COST) which dramatically reduces PAN AIR computer running time is also described It is also demonstrated how this procedure can be used to overcome linear theory limitations at transonic speeds