Elastomer seals are widely used to contain high-pressure gases and can suffer from decompression damage when the contained gas is depressurized. The generally accepted mechanism for the damage is that there is a considerable degree of dissolution of the gas into the elastomer which cannot diffuse out quickly enough when the contained pressure is reduced; hence bubbles and fissures occur in the bulk of the elastomer. Attempts to model this behaviour typically assume the elastomer material properties are measured in the absence of the dissolved gas. In this study, a standard dumb-bell test piece tensometer has been developed which allows the elastomer material properties to be measured while saturated with CO2 and N-2 (two gases with markedly different solubilities) at pressures of up to 4 MPa. The equipment was shown to be capable of providing accurate measurements under these conditions and various fluorocarbon, nitrile and silicone elastomers were tested. These tests showed that the high-pressure CO2 induced a slight reduction in initial modulus compared to tests in air, accompanied by a more significant loss in both strength and ultimate extension. The reduction was greater than 50% in some cases. Electron micrographs of the samples showed that the fracture surfaces were of a smoother nature for the samples tested in CO2, suggesting a mechanism of disruption of interchain forces. The implications of these results for models of decompression damage are noted.