A modified form of the well-known Tsonopoulos correlation for second virial coefficients was developed based on the corresponding-states principle. Comparisons with the new, high-quality experimental data and existing models show that the present correlation is more accurate. reliable and satisfactory for nonpolar compounds. The results also show that the present work is roughly equivalent to the Tsonopoulos and Weber correlations for second virial coefficients of polar fluids. The Weber correlation for the third virial coefficients was also improved since it did not well represent the experimental data of nonpolar gases. The new correlation gives a satisfactory fit for nonpolar compounds as the Orbey and Vera correlation did and can also accurately represent the literature data for the third virial coefficients of polar fluids. which was well represented by the Weber correlation. The two correlations for the second and third virial coefficients need the same additional parameters. such as the critical temperature. critical pressure. acentric factor and reduced dipole moment. (C) 2004 Elsevier B.V. All rights reserved.