The partition coefficients between water and hexane of some n-alkyldimethylphosphine oxides (C_nDMPO) and octylphenyl poly(ethylene glycol) ethers (Triton X-100 and Triton X-405) and of one poly(oxyethylene) cetyl ether (C₁₆E₂₀) have been determined by using an indirect technique based on the measurement of the surface tension of the aqueous surfactant solution after equilibration with the second liquid phase. Though some of the surfactants studied have been described in the past as insoluble in alkanes, the results show that at monomeric concentrations, most of them have a non-zero value of the partition coefficient. These results are particularly important when dynamics adsorption phenomena at liquid−liquid interfaces are concerned.