ASOG (Analytical Solution of Groups), which is widely applied to predict the liquid-phase activity coefficients of solutions, is extended to be capable to distinguish isomers. The Flory-Huggins (FH) part is examined by using the infinite dilution activity coefficient data of n-alkane binary mixtures and an empirical equation is proposed to modify the number of carbons contained in the n-alkanes. The concept of effective carbon number is adopted to apply the empirical equation to components other than n-alkanes. To evaluate the number of group, in the group interaction part, the contact probability is introduced, in which a steric hindrance factor is incorporated. The present model can give a good correlation for the infinite dilution activity coefficients of 1- and 2-alkanols in tetradecane and hexadecane.