Excess molar volumes of mixtures of cydohexane and pseudocydohexane (an equimolar mixture of cydopentane + cydoheptane) with hexadecane and various pseudohexadecanes (equimolar mixtures of tetradecane + octadecane, decane + docosane, or octane + tetracosane) have been measured at 313.15 K. The results for the multicomponent mixtures are compared with those for the binary mixtures and they show that n-alkanes obey, not quite within experimental uncertainty, an extended principle of congruence with cyclohexane as the other component, whereas mixtures of pseudocydohexane with hexadecane do not obey the extended principle.