A series of analytical expressions for predicting and representing ternary thermodynamic properties from binary data have been modified by ternary interaction parameters to describe the binary and ternary liquid systems containing lead. The experimental data of the Bi - Cd - Pb and Sn - Cd - Pb systems at 773K and the Ag - Sn - Pb system at 1073K are found to be excellently represented by the Redlich - Kister Muggianu model including the ternary interaction parameters.