AbstractThe interfacial tension of aliphatic hydrocarbon‐water systems has been found to increase in a linear fashion as a function of the log of hydrocarbon chain length. Contrary to the literature, values of ϕ and े H2dO were observed to be also dependent on hydrocarbon chain length. The relationship between hydrocarbon chain length and interfacial tension is actually opposite to that predicted by Antonow's rule. The results are discussed in terms of hydrocarbon‐water interaction and water‐structure at the interface.