Ellipsometry has been used to analyze the surface of aqueous solutions of hexadecyltrimethylammonium bromide in an overflowing cylinder. The factors affecting the precision and accuracy of the ellipsometric measurements are discussed and ellipsometry is compared with surface tensiometry as a method for studying dynamic interfacial properties. The coefficient of ellipticity was found to vary quadratically with radial distance from the center of the cylinder, in agreement with models proposed in earlier literature. The dynamic surface tension inferred from noninvasive ellipsometric measurements is much higher than previously reported measurements of the dynamic surface tension obtained with a Wilhelmy cylinder.