Abstract The HLD (hydrophilic lipophilic deviation) concept was applied to several water/ i ‐C 13 E n /2‐propanol/hydrocarbon oil systems. For each oil, the optimum formulation, corresponding to HLD = 0, was determined by systematically changing the formulation as a monotonic variation of the surfactant ethylene oxide number ( EON ) scanned variable. The optimum value for EON (symbolized as EON*) was accurately pinpointed both by estimating the solubilization and by measuring the interfacial tension with a spinning‐drop tensiometer. This method allowed the classification of cosmetic hydrocarbon oils such as isohexadecane, paraffin oil, squalane, squalene and hydrogenated polydecenes in C 30 , C 40 , C 40 –C 50 , on an equivalent alkane carbon number (EACN) calibration scale based on five linear alkanes covering the liquid range (C 5 to C 16 ). © 2003 Society of Chemical Industry