In this work we have measured surface tension as a function of concentration of pure and technical nonionic ethoxylated surfactants. CMC values, surface tension at the CMC and the cross sectional headgroup areas are compared. It is shown that the CMC does not depend significantly on the polydispersity of the polyoxyethylene chain. However, the surfactant headgroup area, as determined from the surface tension plots, are much smaller for polydisperse surfactants than for homologue pure surfactants. This is due to the selective adsorption of the shorter polyoxyethylene species at the surface. For the same reason the surface tension at the CMC is lower for technical surfactants than for homologue pure species.