Oxygen transmission rate (OTR) is the measurement of the amount of oxygen gas that passes through a substance over a given period. It is mostly carried out on non-porous materials, where the mode of transport is diffusion, but there are a growing number of applications where the transmission rate also depends on flow through apertures of some description.

It relates to the permeation of oxygen through packaging to sensitive foods and pharmaceuticals.

Standard test methods are available for measuring the oxygen transmission rate of packaging materials. Completed packages, however, involve heat seals, creases, joints, and closures which often reduce the effective barrier of the package. For example, the glass of a glass bottle may have an effective total barrier but the screw cap closure and the closure liner might not.

ASTM standard test methods include:

Other test methods include:

Also a factor of increasing awareness in the debate surrounding wine closures, natural corks show small variation in their oxygen transmission rate, which in turn translates to a degree of bottle variation.