The standard for photochemical oxidants is often exceeded during the summer in the Salt River Valley in the vicinity of Phoenix. Assessment of the photochemical oxidant problem in Phoenix is complicated by relatively low concentrations of nitrogen oxides in the morning, winds that switch direction in the middle of the day, and large changes in mixing height. In this paper, current measurements, modeling efforts, and control strategies are discussed as they apply to Phoenix. Although linear rollback or semiempirical correlations based on smog-chamber or actual measurements are now used to evaluate transportation strategies, better results could be obtained from mathematical air pollution simulation models. The linear rollback analysis currently used by local transportation planners shows that continued inspection and maintenance programs for automobiles and some vapor recovery programs will be required to reduce the maximum photochemical oxidant concentrations in Phoenix to levels below standard. The purpose of this paper is to review the current status of the photochemical oxidant problem in Phoenix and to make projections for the future./Author/