The paper reports the results of an experimental and associated analytical study of the time dependent adsorption of carbon dioxide gas into two nitrile elastomers. The mass gas sorption has been measured using a device based on a vibrating reed to a weight fraction accuracy of ca. 0.05% at 47 degrees C in the ambient gas pressure range 0.1-34 MPa. The experimental method is described and data are provided. These data are used to compute the most effective description of the diffusion process by invoking a number of different diffusion coefficient, D($\theta $), characteristics, where $\theta $ denotes lapsed time, ambient pressure and local ambient gas concentration within the elastomers. The numerical procedures adopted to perform the fitting of the experimental data with various D($\theta $) characteristics are described and the quality of the fit is assessed. The D($\theta $) characteristics chosen have no particular physical basis but follow established empirical precedents. The characteristics of the parameters associated with the various D($\theta $) functions generally indicate that as the gas is embibed with progressively increasing ambient pressures the diffusion coefficient increases. At high pressures the diffusion is arrested and the coefficient decreases. We have associated the initial increase with gas induced plasticization and the eventual decreases with the effect of the hydrostatic component of the ambient gas pressure. The parameter fitting also indicates that the diffusion is arrested with lapsed time which is tentatively associated with time dependent volumetric relaxations. These interpretations apart, the data and analyses clearly indicate that the transport is not simply fickian and a relatively complex parametric function to describe the sensitivity of the diffusion coefficient to time, concentration and pressure is necessary for these systems.