This paper provides a review of the solubility parameter theory and its application to predicting elastomer/fluid compatibility. Emphasis is placed on describing the theory and translating the results of swell data into a more easily understood method than has previously been used. Numerous solubility parameters arc presented as well as swell test details. The swell data results are then used to determine solubility parameters which, upon comparison with other fluid or elastomer solubility parameters, determine compatibility. This procedure is especially important because it enables the results of swell tests to be used to identify elastomer/fluid compatibility of molecularly complex fluid additives or special elastomer mixtures.