A study concerning the importance of molecular weight on the long term performance of one-piece (complex shape) 2-litre biaxially oriented PET bottles is presented. It was corroborated by an early study that the molecular weight of PET decreases with the addition of recycled PET (regrind). Blends of virgin to regrind PET ration of 80:20, 90:10 and 100:0 br weight were used. An investigation was carried out the study the effects of regrind content on performs thermal properties, bottle dimensions, self-standing ability of bottles, base brittleness, and thermal properties of bottles. The long term performance of the bottles with different regrind content levels was also studied under a range of carbonation levels. The results of preform analysis indicate that regrind addition causes no significant changes on the thermal properties and stress orientation of the preforms. The regrind addition were seen to cause deposition of material at the base of bottles. The regrind-blended bottles were observed to have thinner sidewall, and the percent hoop strain of these bottles is larger than the virgins. The base of regrind-blended bottles are thicker, and thus the base creep decreases. The creep resistance decreases with an increase in carbonation level. The crazing are more severe at higher regrind content. But this does not seem to aggravate the base failure. Crazing is also pressure dependent. Thermal analysis on the bottles shows no apparent effect of regrind on the crystallization of the bottle sidewall, however, a decrease in percent crystallinity at the base was observed. The results of the present work, supported by the results of an earlier work, indicate that the influence of regrind on the long term performance of the complex shape 2-litre bottles is not detrimental.