The feasibility of soil vapor extraction (SVE) is, in part, based on vadose zone soil-air permeability. Field, laboratory and empirical correlation methods for estimating soil-air permeability have been reviewed for their appropriateness in determining SVE feasibility, and the development of SVE system design criteria. To better understand the available air permeability test methods, a review of their theoretical development is provided. Empirical correlation methods are available to derive estimates of soil-air permeabilities from soil grain size distributions, hydraulic conductivity measurements or pump test drawdown data. Although these techniques provide data that are of value in determining if the use of SVE at a specific site should be excluded from further consideration, they do not provide adequate data for system design criteria development. Laboratory soil-air permeability tests are also inappropriate for SVE system design because they do not take into account field variability and the non-representative nature of soil cores collected in the field. Most field techniques employed for determining soil-air permeability for surficial soils are likewise inappropriate for the evaluation of contaminant releases that have migrated to depths of greater than one meter. The in situ field borehole permeability techniques used by petroleum engineers, and subsequently modified for use at relatively shallow soil depths, hold the most promise for application to SVE design.