Development of the laboratory-based accelerated service life testing—“tire aging test”—encountered difficulties due to the complexity of multidisciplinary processes in the tire materials and structures while trying to induce thermooxidative degradation similar to that taking place in the “worst case” in-service. Preliminary experience with the oven aging at elevated temperatures showed that in some light truck tires damaging conditions occur in the form of sidewall blisters/detachments and casing separations due to inflation gas built up in interior tire layers during oven aging, even prior the roadwheel endurance testing (DOT HS 810 799, Research Report to Congress on Tire Aging), National Highway Traffic Safety Administration (NHTSA), Washington, D.C., 2007, http://www.cbsatlanta.com/download/2010/0512/23529107.pdf). Analysis and comprehensive modeling techniques are developed for gas diffusion and oxidation in the tire structure, with focus on the intracarcass pressure (ICP) build-up predictions. In finite element models, the temperature dependent diffusion properties are used with account for their high heterogeneity in different tire components. Results of transient simulations predict higher oxidation/degradation rate in the sidewall and a detrimental effect of ICP build-up for Load Range E tires—mainly due to excessive nitrogen permeation. Influence of the butyl liner barrier permeability and gauge is evaluated, as well as impact of other tire construction variations. Predicted trends agree with the available observations and measurements. ICP levels in simulations of the long-term gas diffusion under regular service conditions are significantly lower than in the oven aging test modeling. Mechanical aspects of the ICP-induced sidewall separation are also discussed. Modified aging test conditions are proposed that will greatly reduce the deleterious side-effect of the ICP buildup, as assessed in simulations.