To evaluate the utility of trajectory analysis in the tropical upper troposphere/lower stratosphere, Lagrangian predictions of ozone mixing ratio are compared to observations from the Airborne Tropical TRopopause EXperiment. Model predictions are based on backward trajectories that are initiated along flight tracks. Ozone mixing ratios from analysis data interpolated onto source locations (at trajectory termini) provide initial conditions for chemical production models that are integrated forward in time along parcel trajectories. Model sensitivities are derived from ensembles of predictions using two sets of dynamical forcing fields, four sets of source ozone mixing ratios, three trajectory formulations (adiabatic, diabatic, and kinematic), and two chemical production models. Direct comparisons of analysis ozone mixing ratios to observations have large random errors that are reduced by averaging over 75min (similar to 800km) long flight tracks. These averaged values have systematic errors that motivate a similarly systematic adjustment to source ozone mixing ratios. Sensitivity experiments reveal a prediction error minimum in parameter space and, thus, a consistent diagnostic picture: The best predictions utilize the source ozone adjustment and a chemical production model derived from Whole Atmosphere Community Climate Model (a chemistry-climate model) chemistry. There seems to be slight advantages to using ERA-Interim winds compared to Modern-Era Retrospective Analysis for Research and Applications and to using kinematic trajectories compared to diabatic; however, both diabatic and kinematic formulations are clearly preferable to adiabatic trajectories. For these predictions, correlations with observations typically decrease as model error is reduced and, thus, fail as a model comparison metric. Plain Language Summary To evaluate the utility of trajectory analysis in the tropical upper troposphere/lower stratosphere, predictions of ozone mixing ratio are compared to observations from the Airborne Tropical TRopopause EXperiment. Model predictions are based on backward trajectories that are initiated along flight tracks. Ozone mixing ratios from analysis data interpolated onto source locations (at trajectory termini) provide initial conditions for chemical production models that are integrated forward in time along parcel trajectories. Model sensitivities are derived from ensembles of predictions using two sets of dynamical forcing fields, four sets of source ozone mixing ratios, three trajectory formulations, and two chemical production models. Direct comparisons of analysis ozone mixing ratios to observations have large random errors that are reduced by averaging over 75min (similar to 800km) long flight tracks. These averaged values have systematic errors that motivate a similarly systematic adjustment to source ozone mixing ratios. Sensitivity experiments reveal a prediction error minimum in parameter space and, thus, a consistent diagnostic picture: The best predictions utilize the source ozone adjustment and chemical production derived from National Center for Atmospheric Researchs Whole Atmosphere Community Climate Model. For these predictions, correlations with observations typically decrease as model error is reduced and, thus, fail as a model comparison metric.