Techniques most commonly used for the estimation of the second virial coefficients are based on the corresponding states principle. They are generally semiempirical correlating methods, and their validity is usually limited to nonpolar gases or to small polar molecules. In this paper, an estimation technique for the second virial coefficients based on a modified group contribution method is presented. This method can be applied to a wide range of organic compounds. In fact, the method depends on the knowledge of reduced temperature and acentric factor, and is based only on summing the products of the group contributions and their respective number of occurrences. Each group contribution is derived by analysis of the second virial coefficient data available in the literature.