Fourier-transform13C{1H nuclear magnetic resonance spectroscopy of the internally substituted phenylhexadecanes and theirpara-sulfonates has been done as a part of a general study of alkylaryl sulfonates thought to be of significance in complex surfactants, such as the petroleum sulfonates and various synthetic products. The systematics of structural variations and their effects on observed chemical shifts of specific carbon atoms is detailed with the aim of developing rapid, nondestructive methods of analysis of complex mixtures of both hydrocarbons and hydrocarbon sulfonates. Advantages and restrictions of the13C spectrometric method are illustrated in the case of a mixture of alkylbenzene sodium sulfonates typical of a synthetic surfactant.