Pressure vessels made entirely from fiber-reinforced polymer can generate substantial cost and performance improvements leading to their greater acceptance as a storage medium for pressurized alternative fuels (e.g. hydrogen). Inherent anisotropy and inhomogeneity of fiberreinforced composites usually induces functional failure (i.e. leakage) that precedes structural failure by bursting. Functional failure is attributed mainly to transverse matrix micro-cracking. The complex material behaviour and diverse failure mechanisms associated with composite pressure vessels cannot appropriately be modeled by existing failure criteria. The goal of the proposed project is to develop permeability-based analytical models to evaluate the performance of composite vessels under monotonic and certain fatigue loading conditions.