Starting from the original definition of cohesive energy density and the solubility parameter, a systematic approach is proposed for estimating the latter. The potential energy E and the volume V of the system are obtained from a simple equation-of-state model. The model is able to provide estimations of E and V over extended ranges of external conditions, for pure fluids as well as for mixtures and for simple systems as well as for highly non-ideal systems such as hydrogen-bonded systems, In the latter systems the approach provides estimations of the separate components of the solubility parameter, namely, the "hydrogen bonding" contribution and the "van der Waals" contribution. The estimated solubility parameters compare favorably with widely used tabulated values. The potential of the approach is exemplified by applying it to the estimation of the effect of temperature and pressure on the solubility parameters of mixtures of supercritical carbon dioxide with alcohols as entrainers.