A simplified mean spherical approximation (SMSA), containing only hard-sphere and long-range interaction terms, is proposed. The capability of the model to represent the osmotic coefficients of aqueous electrolyte solutions is demonstrated. The SMSA method yields results that are comparable to the original MSA method but require much less computational effort. To allow the representation of osmotic coefficients over large ranges of temperature and composition, a versatile form of cation diameter has been introduced and shown to yield accurate results. The SMSA model has been used to correlate the osmotic coefficients of 120 electrolyte solutions at ambient conditions and the osmotic coefficients of a group of univalent alkali metal chlorides at high temperatures. In addition, the predictive capabilities of the model were successfully tested on more than 50 electrolyte solutions.