Intermolecular potentials are determined using ab initio and experimental data. The strongly structured contributions are obtained from molecular parameters, which are determined by probing the molecular shape and the static potential. The remaining attractive terms, which are more isotropic, are then evaluated through a fit to experimental data such as second virial coefficients B(T). The method is applied to CH4, CH3F, CHF3, CH3Cl, CH2Cl2, CH3CN and CO2 and the corresponding site parameters are reported. The resulting potentials are compared with others proposed in the literature.