The EKMA was evaluated using applications in the Tulsa area primarily by comparing the trajectory model that forms the basis of the EKMA (OZIPP) with other, more sophisticated, models. The study was carried out at several levels, beginning with evaluation of OZIPP and ending with an evaluation of the control-strategy predictions that result from employing the EKMA isopleth methodology. The OZIPP trajectory model was compared with the SAI Airshed Model and the SAI trajectory model, as well as with some modified versions of the original OZIPP model. The basic OZIPP model is a simple, moving-air parcel, or trajectory, model that uses a detailed chemical mechanism for the surrogate propylene and butane hydrocarbons. The model treats time-dependent, precursor-emission factors along with expansion of the air parcel; entrainment is treated by assuming that constant concentrations exist outside the parcel. The primary emphasis of this comparison study was directed toward the discovery of features in the basic OZIPP model that could explain differences in the results of the OZIPP model from those of some other model.