Poly(ethylene terephthalate) (PET) bottles are commonly used for packaging of carbonated beverages. Stress cracking in the petaloid-shaped base of the filled bottle has been costly to the beverage industry. This study compares the performance of a standard bottle and a bottle with a base geometry optimized against environmental stress cracking (ESC). The crystallinity of the bottle base is evaluated across the base diameter for both bottles. Moreover, to explain the mechanism of the crack formation and propagation, the cracks in the bottle base are investigated through environmental scanning electron microscopy (ESEM) and optical microscopy. Top-load strength, burst strength, and thermal stability are also reported. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 3811-3818, 2009