The permeation of initially pure methanol into > 95% relative humidity air has been demonstrated with three membranes, supported poly(1-trimethylsilyl-1-propyne) (PTMSP), supported poly (dimethyl siloxane) (PDMS), and a 125-mu m polysilicone film. Although fundamentally similar to pervaporation, the arrangement entailed small scale (similar to 1 cm(2)) membrane dispensing of methanol with water counterdiffusion. Volumetric readings over time, final concentration measurements, and subsequent parameter fitting to a derived first-order mathematical model revealed high selectivities - 8.4, 10.3, and 8.3 for the respective membranes - for delivery of methanol versus uptake of water. These selectivities represented factors of 1.5, 1.9, and 1.5 beyond the relative saturation vapor pressures of methanol and water, perhaps, as a result of a favorable inhibition of water counterdiffusion by methanol permeation. Initial methanol permeation rates of 380, 730, and 260 g/h m(2) were also estimated. A transport mechanism adjustment is suspected with PTMSP because of a slightly more rapid permeation rate decrease than indicated by the model. The experimental arrangement and mathematical model provide a new general framework for evaluation of membranes and designs for potential dispensing applications. (c) 2006 Elsevier B.V. All rights reserved.