The phase behavior of surfactant-oil-water systems is affected by the so-called formulation variables, i.e., by the nature of the components or their physicochemical characteristics. One of the formulation variables is the alcohol effect, which accounts for the type and concentration of alcohol. In most cases the addition of a lipophilic alcohol contributes to the increase of the amphiphile mixture lipophilicity at the interface, which results in a WI --> WIII --> WII transition, similar to the-one observed when the water salinity is increased. However, in some cases the Winsor II phase behavior is never reached with the alcohol content increase, and a WI --> WIII --> WI so-called retrograde transition is exhibited instead. Such an anomalous case is analyzed here for a system containing a commercial nonionic polyethoxylated surfactant, n-heptane, water, and n-pentanol, the concentration of the latter playing the role of the formulation variable. HPLC analysis of the different phases indicates that the surfactant oligomer partitioning between phases is affected by the alcohol content. The retrograde transition due to the increase in alcohol content is shown to come from the strong increase in the partitioning of lipophilic and balanced oligomers into the oil phase, with the remaining surfactant, in particular the interfacial mixture, becoming more hydrophilic.