The values of s activity in the liquid s-fe-co-ni system were determined from unpublished equilibrium data for h2 + s (in alloy) = h2s. The activity coefficient of s ranged from 0.387 to 1.896 And increased with increasing concentrations of fe and carbon monoxide. The published values for the activities in the binary systems fe-co, fe- ni, and co-ni were used to calculate the activities in the ternary fe-co-ni alloys, and the results were expressed as a funciton of composition. This function was used with the activity coefficients of s in the binary metal solvents to express the activity coefficient of s in the ternary metal solvents as a function of mol fractions of fe, CO, and ni. The experimental values for s in fe-co- ni agreed well with the calculated values based on the binary metal solvents, and this showed that all the activity values were consistent.