Abstract An experimental design on a Starks' matrix (seven factors, at three levels) has been carried out to confirm the correlation expression for optimum formulation of non‐ionic surfactant–oil–water systems. The linear variation of the average number of ethylene oxide groups per surfactant molecule at optimum formulation versus alkyl chain number, temperature, salt and alcohol concentration validates the postulated first order model. Moreover, the proposed method for the determination of the eight coefficients of the model only requires 16 experiments and is an alternative to the classical two‐dimensional scan strategy. © 2003 Society of Chemical Industry