In the lungs, oxygen transfer from the inspired air to the capillary blood needs to cross the surfactant lining layer of the alveoli. Therefore, the gas transfer characteristics of lung surfactant film are of fundamental physiological interest. However, previous in vitro studiesmost relied on the Langmuir-type balancefail to cover the low surface tension range (i.e., less than the equilibrium surface tension of approximately 25 mJ/m(2)) due to film leakage. We have recently developed a novel in vitro experimental strategy, the combination of axisymmetric drop shape analysis and captive bubble technique (ADSA-CB), in studying the effect of surfactant films on interfacial gas transfer (Langmuir 2005, 21, 5446). In the present work, ADSA-CB is used as a micro-film-balance to study the effect of compressed bovine lipid extract surfactant (BLES) films on oxygen transfer. A low surface tension ranging from approximately 25 mJ/m(2) to 2 mJ/m(2) is studied. The experimental results suggest that lung surfactant films at a low surface tension near 2 mJ/m(2) provide resistance to oxygen transfer, as indicated by a decrease of 30-50% in the mass transfer coefficient (k(L)) of oxygen in BLES suspensions with respect to water. At higher surface tension (i.e., > 6 mJ/m(2)), the resistance to oxygen transfer is only modest, i.e., the decrease in k(L) is less than 20% compared to water. The experimental results suggest that lung surfactant plays a role in oxygen transfer in the pulmonary system.