Densities have been measured for mixed aqueous solutions of N-methyldiethanolamine (MDEA) and diethanolamine (DEA) at 25, 30, 40, 50, 60, 70, and 80-degrees-C. The compositions of the ternary solutions are near 30 mass% solute, because of industrial applications for the absorption of acid gases. The isopycnotic (same density) method, for predicting densities of multicomponent aqueous systems at 25-degrees-C has been used to predict the densities of the present non-electrolyte mixed solutions at other temperatures. Predicted and observed density values are in good agreement (< 0.06% error). The method has also been used to predict densities of some aqueous sea salt mixtures at temperatures ranging from 5 to 95-degrees-C. Again the predicted and observed values are in good agreement (generally < 0.1% error).