Micropipet aspiration was performed on unilamellar vesicles to study the effect of ethanol on lipid bilayer mechanical properties and area per lipid molecule. We show here that fluid-phase SOPC (1-stearoyl-2-oleoylphosphatidylcholine) lipid bilayers in a water/ethanol solution (5-20% ethanol vol:vol) have significantly decreased area compressibility moduli, bending moduli, lysis tensions, and lysis area strains in comparison to SOPC lipid bilayers in a water solution. We convert the area compressibility moduli into bilayer interfacial tensions through simple linear relationships. The SOPC bilayer interfacial tension decreases as the ethanol concentration is increased. We attribute the total interfacial tension. reduction to a quantifiable adsorption of ethanol at the SOPC bilayer-aqueous interface in addition to bulk interfacial tension reduction. We use the interfacial tension reduction to estimate the increase in the area per lipid molecule (area expansion) of the bilayer as the ethanol concentration is increased. We then directly measure the area expansion in a separate set of micropipet experiments and find good quantitative agreement with our estimates. We observe that the SOPC bilayer surface area (area/molecule) expands laterally when the surrounding media is changed from an aqueous solution to an aqueous/ethanol solution (e.g., 9% area expansion when the media is changed from a water solution to a 20% ethanol-water solution).