Relationship between various transport parameters (diffusion and permeability coefficients, and activation energy of diffusion (ED)) and cohesion energy density (CED) of polymers are considered on the basis of Meares equation. It is shown that the distances between neighbor free volume elements (FVEs) in polymers found via positron annihilation studies are in reasonable agreement with the diffusion jump length as estimated using Meares formula. In this way, a mean concentration of FVEs was estimated as (0.3 +/- 0.1) x 10(20) cm(-3). Meares formula explains also several empiric correlations, such as correlations between E-Di and E-Di for different gases (i and j), relationship between permeability coefficients and fractional free volume (FFV) and CED.