The objective of this work is to study the gas/vapor sorption in poly(lactic acid) (PLA) with a 98:2 (L:D) ratio using a quartz crystal microbalance (QCM). For that purpose, the sorption of carbon dioxide, ethylene and water vapor in poly(lactic acid) (PLA) with a 98:2 (L:D) ratio, in temperature range from 283 to 313 K and up to atmospheric pressure was measured. The measured isotherms indicate that the sorption mechanism is sorbate dependent, since carbon dioxide and ethylene seem to have predominantly a Langmuir type of mechanism while water is predominantly Henry controlled. Two temperature protocols were used and only ethylene sorption is affected by them. Comparisons with previously measured gas sorption data in PLA 80:20 using the same temperature protocol indicate that the L:D ratio plays a dominant role in gas/vapor sorption in PLA. (c) 2006 Elsevier B.V. All rights reserved.