Thermally formed thermoplastic articles can be protected from stress cracking in the presence of stress cracking promoting compounds by forming a shaped article comprising a thermoplastic and a liquid hydrocarbon oil composition. We have found that the liquid hydrocarbon oil composition prevents the stress cracking promoting materials from interacting with the polymeric structure of the stressed container to prevent or inhibit stress cracking in such materials. The methods and compositions of the invention are particularly useful in preventing stress cracking in polyethylene terephthalate beverage containers during bottling operations during which the bottle is contacted with aqueous and non-aqueous materials such as cleaners and lubricants that can interact with the polyester to cause stress cracking particularly in the container base. A process for lubricating a container, such as a beverage container, or a conveyor for containers, by applying to the container or conveyor, a thin continuous, substantially non-dripping layer of a liquid lubricant. The process provides many advantages compared to the use of a conventional dilute aqueous lubricant.