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The methods based on the Group Contribution Concept usually fail when one attempts to estimate the physico-chemical properties of different branched isomers of a given compound. We present a new concept, the Group-Interaction Contribution Approach (GIC) which considers the contribution of the different interactions between groups present in a molecule instead of the contribution of structural groups. This approach allows differentiation between branched isomers, thus leading to different values of the physico-chemical properties. The GIC Approach can be easily implemented in current correlations based on the group contribution concept. The estimates of enthalpy of formation, normal boiling temperature and critical temperature of a series of 51 saturated hydrocarbons showed clearly that the GIC concept leads to very good estimations for branched isomers.