The aim of this article was to evaluate and analyze the mechanical properties of bonded elastomer discs subjected to triaxial stress on an MTS (machine for testing samples) equipment. Several pulling tests were run on an Instron machine using an O-ring type of samples to evalutate the mechanical properties of testing unfilled nitrile rubber subjected to uniaxial tension. It was found from the stress-strain curve of the O-ring samples that a very small stress softening occurred when the maximum strain is less than 200%. It was also found that the stress and strain at break does not drastically vary with respect to strain rate. The initial modulus does not vary with respect to strain rate up to epsilon = 2 min(-1), and only for large values of epsilon does the modulus depend on the strain rate. The material used for the uniaxial tension experiments were bonded between two rigid cylindrical steel plates and the specimens were subjected to uniaxial tension on an MTS machine. It was found that the initial modulus in tension was smaller than in compression. The theoretical predicted initial modulus from Gent’s equation was much larger than experimentally estimated. It was shown that the elastomer in the pancake tests was not incompressible and a value of 0.494 was determined for the effective Poisson’s ratio. A mathematical equation was derived for the effective Poisson’s ratio as a function of the volume fraction of voids within the testing material.