Six chemical reaction mechanisms for photochemical smog were analyzed to determine why, under identical conditions, they predict different maximum ozone concentrations. To perform the analysis, a counter species technique was used to determine the contributions of individual reactions or sets of reactions to the overall behavior of the chemical reaction mechanism. Using this technique, answers were obtained to previously inaccessible questions such as what is the relative contribution of individual organic species to photochemical ozone formation. Based on the results of the counter species analysis specific aspects of each mechanism were identified that are responsible for the discrepancies with other mechanisms. For each mechanism, parameters were identified that when altered brought the predictions of the various mechanisms into much closer agreement.