AbstractSorption measurements of CO2, Ne, and Ar in poly(butylene terephthalate) (PBTP) films were studied by the gravimetric method with a recording microbalance at 298 K in the pressure range of 1–22 bar. The semicrystalline samples were annealed and oriented at 373 K. The sorption isotherms for CO2in PBTP films in the glassy state can be well described by the dual‐sorption theory. The nonlinear sorption behavior of Ne and Ar can be satisfactorily analyzed using the sorption model developed for noble gases in PBTP. For the undrawn annealed films, it has been found that the increment of crystallinity leads to the reduction of the equilibrium gas concentration. For the oriented films, the gas concentration rises with increasing draw ratio. It appears that the sorption behavior for all tested gases in the oriented PBTP films does not depend on the changes of crystallinity and crystalline morphology under extension. The difference of the critical pressurep*indicates the change in the size of the frozen microvoids existing in the noncrystalline phase, which was altered by annealing and drawing. © 1993 John Wiley&Sons,