How can PET have a positive environmental profile if its raw materials are petroleum-based?

PET is a remarkably energy-efficient packaging material.  First of all, it's highly recyclable.  Although the feedstocks for PET are crude oil and natural gas, the environmental impact of PET is very favourable in comparison to glass, aluminium and other container materials.  Because PET is so strong yet light in weight, it allows more product to be delivered with less packaging, less weight and less fuel are required for transportation.  Life cycle studies of PET have consistently shown it to be a highly sustainable material with a positive environmental profile.