Supercritical fluid chromatography (SFC) is capable of separating oligomers of alcohol ethoxylates (AEOs) and propoxylates (APOs) samples with pure carbon dioxide. The instrumental conditions, however, needed for separation necessitate both high temperature and high pressure. Derivatization of alcohol polyether samples with an UV absorbing agent has been achieved with a phenylated disilazane in hopes of employing a solvent-modified CO2 mobile phase in conjunction with both lower CO2 pressure and lower temperature for oligomer separation. A silylether containing a single phenyl group was formed via the derivatization of the hydroxyl termini of AEO and APO samples. The derivatized polyethers were detected at 215 nm with little or no interference from the mobile phase. Octadecylsilica (ODS) and a polar embedded alkyl bonded silica stationary phase were studied with the organic solvent-modified CO2 mobile phase. The combination of an ODS phase and the polar embedded phase, tandemly stacked, produced the best chromatographic separation of oligomeric species. Data from SFC-UV separations combined with peak assignments from SFC with electrospray ionization-mass spectrometric (ESI-MS) detection produced average molar oligomer values for each surfactant sample.