AbstractAn intensive study of the mass spectral characteristics of straight‐chain alkylbenzenes has been made in conjuction with their ultimate performance as sulfonates in heavy duty formulations. Two variables of the alkylates, carbon‐chain length distribution (which fixes the mean mol wt) and phenyl position on the chain, have been successfully related to the observed dishwashing performances. Formulas are given which allow accurately predicting this performance criteria. The important role of phenyl position is illustrated by a detailed study of each phenyl isomer in the tetradecylbenzene series.