A reliable new three-dimensional potential energy surface is obtained for the H 2 -Ar system using an exchange-coulomb potential model with five parameters determined empirically from a least-squares fit to experimental data. This surface fully accounts for new high resolution IR data, virial coefficients, and vibrational transition pressure-shifting coefficients used in the analysis, and yields excellent predictions of elastic and inelastic scattering cross sections and hyperfine transition intensities not included in the analysis. Quantitative comparisons with the best previous empirical potential and a high quality fully ab initio potential are also presented.