Abstract : The Air Force Research Laboratory requires a method for predicting the relative life of O-rings produced by different manufacturers. O-rings manufactured to the same MIL-spec from different manufacturers usually use different material formulations. Differences in formulations can result in different properties as the O-rings age. The required test methods would be based on benchtop procedures capable of determining basic properties of new and aged seals, which affect sealing properties. Two methods potentially capable of measuring the storage and loss moduli of O-rings under dynamic conditions were proposed. One method was based on measuring multiple rebounds of a pendulum dropped against the O-ring The second was based on determining the force displacement response of O-rings squeezed between two parallel plates and excited over a series of frequencies ranging from 1 to 100 Hz. Test instruments were built to explore both methods. Silicone and nitrile O-rings from multiple manufacturers were aged under different temperature and pressure conditions for 168 and 504 hours to provide the test samples. Computational methods were developed to analyze the data from these test methods. Two computer code versions were developed. The first was designed to run on a PC, and predicted the deformation and forces for O-rings for a variety of loading conditions. The second was a workstation version that automatically ran either of two finite element codes (MARC or ANSYS). The workstation versions have much more capability than the PC versions, but of course are more difficult to run. The test methods both proved capable of measuring the basic properties of the O-rings, with somewhat greater accuracy from the pendulum rebound method. Variations between different materials were determined. However, the aging method did not induce significant changes in each family of O-rings, preventing development of a true life prediction method.