The activity coefficients gamma of benzene, hexene, cyclohexane and hexane in mixed solvents morpholine-dimethylformamide and morpholine-cellosolve have been determined in the entire hydrocarbon-mixed solvent concentration range. The results have been described by the simplex grid method with a fourth-order polynomial. The existence of synergism on the curves of selectivity and dissolving power of the solvents has been established. The extraction properties of the mixed solvents investigated have been assessed.